I always overspent so probably not the best person to comment. Mine are teenagers so it's difficult not to spend much as even a few presents costs £££.
If they didn't play with a lot of last years then maybe you need to focus on things that they need and things they enjoyed. Obviously all children are different, but at that age mine were really getting into lego and that's a gift that can be built on for birthdays and christmases in the future. Do they need a bike or scooter? Balls are usually good becasue they get used but don't last. What about a bigger gift of something for the garden, trampoline/swing set?
Consumables such as play doh and craft stuff which gets used up. Books and kiddy toiletries? Do they need new PJs or slippers/dressing gowns? Dressing up things? Lots of things you can bulk up to make it look like a larger pile without it being stuff that wont get used as that's just wasted money and clutter. Oh and you can never go wrong with a torch for some reason. :)
I've no idea what is affordable for you and cant remember what I used to spend (but it was too much really).
What did you spend last year? What are they interested in?