I don't even know how to deal with this. I can usually only sell my art for like $3 and lord knows I can't sell my prints.
Really? I see stuff like this at anime cons go for more than that. Of course, it's been a few years since I've been to one, but cheapest prints I see start at like $5. From there, it goes up from size, pic content. Most prints that're higher in price have backgrounds of some sort.
It's certainly possible to have one that doesn't have a background go for that, but has multiple characters in it. I don't think I generally see single pics, without a background of any sort go for that. Mainly since it just doesn't look as good on your wall. That's an aesthetic thing, but depending on the content of the pic, the lack of a background (as in just a solid color) could be a deal breaker.
Probably won't be if they like the art enough, but always something to keep in mind when selling art at cons. I've only sold physical crafts, like phone charms and plushies at cons, not prints, but from a buying standpoint, even if I like a piece, if it seems incomplete, I don't buy it. Of course, if the background doesn't remotely go with the art, that's just as bad as having no background.