melika - if you are struggling, you have no option but to skimp on presents. The priority is getting the mortgage paid, and food on table. DC still get lots of days out with mum and dad, even if it's the beach or local park/ woodland walk, rather than zoo.
We have young children, and £40 is not a problem. My DD1, loved her second hand play den last year. It's just a case of looking for offers, and sometimes buying second hand. DVD's, arts and crafts stuff, flower press, junior gardener mini greenhouse /propagator kit, scooter, playmobil farm, books, activity table, childrens chalkboard, second hand swing for garden....
I have no experience buying for teenagers, and might have to increase budget to £60. I don't see that they will need designer labels or status symbols though. I'm sure they'll survive childhood without an iPad.
I'm not against going crazy now and again, if they really really wanted a Kindle Fire, I'd save up to get it, just not every year. We have stretched our budget for bigger items, such as a bike already, but it's not an every year expense.