My younger DD is in first grade. $10 is very acceptable for a birthday present. If you get webkins, Walgreens has buy 1 get 2 free on Black Friday.
I like to buy books as gifts as well as fun jewelry. If you have a Claires around, they often have sales on bracelets, necklaces and hair stuff that little girls love.
Some suggestions for books would be the Curious George Christmas or other book that Kohls has for $5 right now. It's hard back and really nice. Also, both of my girls like Junie B Jones and Magic Tree House. You can get either book in paper back. They each have a bunch in their series and are nice read aloud chapter books that the children will be able to read by themselves later on.
We go to lots of parties too, so when I see an item on clearance, I pick it up. That way we can give more and still stay around the $10 amount. But most times, both of my girls go, so then I try to give two gifts...