I think $25-$50 is a good guideline to go by. However, if you just can't afford that much, then do whatever you can. There have been times, when I was a lot younger, that all I could really afford was a $15 gift (and that was almost overdoing it for me), but nobody made me feel guilty about not spending more. It really should be the thought that counts, not how much money you spend and people should be appreciative of just having you there to share in their happiness.