It's perfectly OK to give up pretty much any rights to the story, as long as you feel you are being justly compensated for them. If I were to make such a sale, as a no-name writer I wouldn't expect to get a large amount of money, but that's OK. Stephen King, on the other hand can reasonably expect a larger sum for his efforts.
If you can't afford a lawyer (it's a short story, so I'm betting you don't have a lot of cash left over for lawyering after you buy Ramen), then read it carefully and make sure it enumerates, with precision, the rights you are giving up, and how and when you are to be paid.
You might also want to try to get some kind of 'reversion' clause on any rights where that makes sense. For instance, with first publication rights, it doesn't make sense to have reversion clause - but if they retain the sole right to reprint the story, you'd like for that right to revert to after some period of inactivity (several years at least).
If you can get it you'll also want some kind of reversion clause for the case where they don't actually ever publish at all. Again, this would be a several year timeout, but if something goes wrong after you've been paid, you eventually want the story to see the light of day.