Usually, it's both. But initially, it starts with the face value and the body. Of course, no one likes f***ing an ugly person unless you're desperate to get laid. If the girl is really good in bed, then that would be money well spent.
As for the price, that's really up to you. You can try to haggle for something reasonable. Some newbies could give in, but those who've been around the block will not entertain your haggling and will simply tell you to f*** off. Some guys are willing to pay 5k just for 2 pops, but that means the girl is worth it. Of course, some guys would want to get feedback first if the girl is indeed worth the dough