We don't do punishments or rewards. I don't think that Christmas gifts should be tied to how much you 'like' your kid's/behavior. I think that if you show unconditional love and consistently model good behavior, they'll do what you do. But I'm not having a pop op, I understand where you are coming from, and I know it's difficult in practice.
Dss is our only teen, we usually spend about £150 on him, his mum spends a lot more (she's got a lot more money), then grandparents etc. Last year we were pretty skint so we spent a lot less. Interestingly, he brought it up a couple of weeks ago and told me that he'd loved everything we'd gotten him last year because it felt like we'd really thought about what he liked, in contrast to his mum, who'd spent probably 3 times as much, but who he didn't feel took much interest in what he liked. He's a sensitive kind of guy!
I don't think any amount is too little or too much, it just depends what you can afford. I like having a lot of toys for the kids, they get a lot of use out of them, so I spend as much as I can afford. If you approve of the thing itself, can afford it, and believe it will make him happy, don't not buy it to punish him, it's manipulative and not in the spirit of Christmas!