The consequence is too big, and most likely also the gap between your child's current behaviour and your behaviour expectation - as evidenced by the fact that you keep running out of consequences and have nothing else to take away. This will render it totally demotivating because he has nothing to behave for. Five chances per week is ludicrous - everyone makes more than five mistakes a week, and he's a child with a neurodevelopmental disorder.
Some "attitude" is likely literal thinking and/or a stress response and/or not understanding social cues. Some autistic children also don't "see" hierarchy and will find it inherently unfair when adults expect children to defer to them. They expect to have the same rules for everybody - which I do think is fair TBH, although sometimes there are good reasons for different rules (e.g. earlier bedtime for children). But certainly often adult tone towards children can be quite directive in a way which is not considered acceptable from children to parents. Autistic children sometimes do not understand this and will model or mirror that tone. It can be worth bearing this in mind.
By having really big consequences that you are intending to hold over him as a threat, it is likely priming him to respond as though he is experiencing threat, which is why you get the defensive "What are you going to do?/I don't care" response.
It helps to get really specific about what behaviours you want to change (and try to go to the root rather than the reaction, so e.g. if you are getting "attitude" when you ask him to come off electronics, then coming off electronics is the behaviour to address, not the attitude).
Use very small minor token consequences. Like take 10p off him instead of £1. Don't have a tipping point where it all goes. Consequences don't change behaviour on their own anyway, and the effect of a small consequence is just as impactful as a larger one, the only benefit of an extreme consequence is that if the child is genuinely afraid of it, you are more likely to get compliance in the moment. But aside from the two obvious problems with this - if you're going with fear, that's dangerous in terms of where you end up, and the other problem, if the child is behaving in a way they can't control (e.g. meltdown) then it won't work anyway. And even if it does seem to gain compliance in the moment, it still doesn't help with long term patterns of behaviour change (according to research).
Since using fear is a risky and not very effective approach, the main purpose of a consequence in the moment is to give parents something to do to replace emotionally driven behaviour responses such as shouting, threatening, intimidating body language etc, all of which will just escalate a child. Whether or not it's related doesn't actually matter, whether or not it helps you to stay calm and unemotional is what matters. Trying to keep everything related might mean deciding in the moment, which is likely to conflict with the calm/unemotional/reasonable aim, and can also be unpredictable which can be confusing and upsetting for autistic children who will probably perceive it as unfair if a behaviour gains X consequence one time but another time is ignored or receives Y consequence. Unless you can decide a specific consequence for a specific behaviour in advance and have this as a stated, consistent rule (e.g. coming off game time with rudeness means reduced or lost game time tomorrow). But this can become complicated.
For all children, but particularly autistic children, it helps if the behaviour expectations are clear. So you should know what the behaviour is that you are trying to change and what your expectation is. To use the example of coming off electronics when time is up, the expected behaviour might be that when the time is up (and there should be a clear way to communicate this), DS will find an appropriate point to save and close down the game ASAP without complaining or shouting about it.
If the behaviour expectation is clear, it makes it much easier to notice and reward (e.g. praise) when you see this behaviour, which is much more effective in changing behaviour anyway.
If the behaviour is not moving towards the expectation, the instinct is often to increase the severity of the consequence - but it's actually more effective to keep the consequence very minor and instead add stepping stones between the current behaviour and the expected behaviour. If there is still no progress, reduce the distance between the stepping stones rather than increase the consequence.
For example a child who struggles to come off a game and becomes violent and makes rude comments and shouts might need this breaking down, so you ignore the verbal stuff for now and only address the physical. Once the physical violence is under control then it makes sense to address the verbal aspect and this might also have to happen in stages, e.g. if your child is screaming I fucking hate you, I am going to put you in the bin, you might want to address individual words first and then the violent intent of the phrases and then the volume and tone only last of all. Or volume then threats - depends what you consider more of an issue. But if you have decided to address violence and then your child mutters "I hate you, why are you always so MEAN" then it is counterproductive to address that kind of verbal outburst when this is a vast improvement over being violent, and it may have taken them considerable effort to make that improvement. The stepping stones and recognising success are hugely important. There is a very good free course on Coursera called ABCs of Everyday Parenting which goes over reward vs punishment, scaffolding and so on. It's designed for use with "challenging behaviour" which includes ND conditions although obviously bear in mind you can't discipline autism away. It does also help to learn as much about autism as possible to understand some of the behaviours.
De-escalation can help if you have a child who is easily escalated, which a lot of children with ASD are, in effect if you are getting heated emotionally in response to their escalation, which BTW is a totally natural, instinctive response and it is very hard to avoid this (which is why you do all the prep for what to do in the moment instead of exploding) - you are "co-regulating up" which is the opposite of what you want, you want to co-regulate them down to a calmer, more reasonable place. NVR is good for de-escalation techniques, and I have heard great things about the books by Linda K. Murphy.
If you're also thinking about which behaviours to address in advance then you can try to also look at the problem from the child's point of view, which often helps reduce conflict and "attitude" drastically. Ross Greene (e.g. The Explosive Child) is fantastic for this with a whole framework for how to have conversations and get their perspective about what's difficult. To borrow the game example again, for example a child may be able to tell you that it's hard to come off the game because it feels like the time warning comes out of nowhere and they can't believe it's been a whole hour. In that scenario, something like a visual timer so they can see what time they have left might help, more than trying to punish their expression of their feelings about this sudden intrusion.
Or they may get several short gaming sessions per week but feel that this is frustrating because as soon as they get into something, it's time to stop playing. In that scenario, it might make sense to consolidate all gaming sessions into a longer session e.g. at the weekend.
If you tried to solve for problem A and the child is actually having problem B or vice versa, the solution probably isn't going to work very well, which is why it's important to actually talk to them or try to gain their perspective another way.