MP's right, there's a LOT of prep involved with concrete floors, and if you have to throw a warranty on top of that, you need to add it to the price somehow, because odds are as good that the epoxy will fail as they are that the concrete will crack...
Even the newfangled latex-based floor epoxies, though convenient and less hazardous, involve the same prep--That 'crete's gotta be eat-off'n-it clean...And etched correctly.
If you haven't done floors before, you're going to learn a few things at $4/ft. Once the floor is
properly prepped, the material is a matter of preference, IMO...
Good luck