I didn't want to spend too much, I think I spent about $30ish per bag. I set that budget because I figured I was spending a LOT on the party anyway, and I'd been to parties where they'd obviously spent more but most of the stuff, we probably wouldn't use anyway.
I got:
a ball - I found 3 for $10, I know that my daughter LOVES that kind of thing, and I've had comments from guests who their kid loved it too. And I figured for $3 each, it's not bad
a book - I found a set of 6 little cardboard books, I think the set of 6 was about $60 or something each (could be wrong), so about $10 each. I don't think it's obvious that I split up a set, and it's something that can be kept. Although my daughter used hers as a teething toy
some food stuff - I split it by age, and bought some age appropriate snacks, boxes of raisins, little biscuits, etc
a couple of balloons - all kids love balloons!! I just put them in loose so they could use them whenever they want.
I think, if you want to spend $100 or more each, go for it - but you don't HAVE to spend that much. Particularly (I think) if you're paying a lot for the party anyway. If you want to spend less, you just need to shop around and be smart about how you spend the money. YOU set the budget though and don't let peer pressure dictate what you "should" spend.