Teen not understanding how much things cost...

[HeyUpDuckie]

This month has been expensive Ive already spent £300 on my teen this month so he could go to London on a residential.
He's now asking me for £60 to go out with his mates tomorrow to do some activity along with a lift (its a hours drive.)

I don't have the funds for this Ive tried to explain its before pay day and I dont get paid yet so its not possible and to try and arrange something after but hes not having it. He has autism and struggles to understand the concept of money as does his mates.
I remember being a teen and just hanging around my mates houses but my sons mates always want to go out and do really costly things.
Aibu to say no this one time?

So he says 'you've got the money, you're just being mean'
What do you say in response to that?

No he won't be. It's easier for his mates as they live by there, so don't have to factor in the cost of petrol either. I can't even drop him off and come back as it's a hours drive and then i need to do something with his brother while he's seeing his mates. It's the bigger picture of things hes not seeing. I have no issue him seeing his mates, it's great but they have no consideration of time and planning. I am surprised their parents haven't mentioned it to them either.

He does preparing for adulthood but I dont know if they've really explained about the cost of things etc.

I don't think that "preparing for adulthood" is something you can outsource to an education provision and expect excellent results.

How often does he get his allowance?
Start weekly for a while
Then ten days maybe
Then two weeks
Leave it at 2 weeks for a while
Then 3 weeks
Then months

Sit down with him and plan what he'd like to spend it on. Write down how much all this comes to. Get him to work it out
If it's more than his allowance help him work out what to cut and what to save for

Back in the day when family allowance used to be £7odd a week, my mum used to give it to me once a month for clothes. Yes I'm that old. Anything over that amount I needed to spend had to come from my savings