On principle, if you go, you should give at least a TOKEN gift of some type. Go into Amazing Savings and buy a candy dish or cake plate for $5-10, for goodness sake. It will not cost much. I would never, even if poverty stricken (and I have been, at times),walk into a simcha empty-handed. Some people even give a gift when they could not attend (but I think you can fudge on that one, if you are financially challenged).
Posters are also correct that contributing to Sheva Brachos or a limo (a new shtick these days, G-d knows why), or being part of a group gift of some other type, are all viable ways to participate without emptying your wallet too badly.