An Epoxy Garage Floor Coating Is Cheap, So Staining Is Even Cheaper, Right?

Usually, but not in this case. My guess would be that it's due to the acids needed for the etching process, but a can of Quikrete Etching Stain will likely run you over $300, and that's without cleaner or sealant. That's pretty darn expensive, even moreso than some of the higher quality garage floor tiles. However, garage floor tile won't make your concrete look like marble. Is it worth it? That depends entirely on you. If protecting your concrete is your top priority, I would say no, although once sealed, there is some protection. If your main goal is to make your concrete look different than any of the other garage floor finishes, though, then this will certainly do it.