I have a general idea of what we have in the budget. It isn't a set cap per se, but a range. They do not get everything they want (could anyone possibly, ever?), but we try to accommodate their most desired item if it isn't something we are opposed to them having. For example, son wants a lift kit for the vehicle he is driving. We won't be spending money on that b/c we really don't want him to have that.
Last year, he got a phone. He'd been wanting one for several years, but last year was when it became something that was more needful and helpful to US as the parents, rather than just something he *wanted*. So he got it last year.
This year, he doesn't have much on his list, and what is there is expensive (Costa sunglasses anyone?) I don't think a 16 year old needs a $200 pair of sunglasses just because it's Christmas. His tastes will change in 2 months and he'll want a different kind.
But, kids need clothes, and this time of year there are always massive sales on them at their favorite "teen" stores. So they will get a good bit of clothes. Less because they ask for them, and more because I will be buying them clothes anyway, so why not get a deal and have them under the tree to open on Christmas morning?
Daughter wants a flute. They aren't cheap. I've done my research, scoured online, been into music shops, etc.. found one on CL, had it checked out by her band director, and bought it. That will be her "big" gift this year. It isn't something she needs. She plays in the band, but on another instrument, so this is just to play around on. It's still a very nice gift. She also is a voracious reader, and is constantly asking for books. So she is getting some of those, and lots of clothes.
When I feel "done", I will make a list and see if there are relatively similar numbers of items for under the tree, and supplement from that. No matter the pricing/value, it is sad to have 25 gifts under the tree for one person and 5 for another. So that doesn't happen at our house. If I have to buy socks and wrap them, I buy socks and wrap them. :)
Good luck. And Merry Christmas!