People are often shocked by the costs, but seems to me, that they're looking at it the wrong way.
You pay for art that is of commercial grade quality, done by people making a living out of doing that art, so ofc its gonna be really expenisive.
Question should be, what are you going to do with it?
If you're not running a (successful) Kickstarter campain, already have massive funds or atleast already some sort of reputation, you hardly would sell enough games, to even cover to expenses for a full custom game.
There are so mayn good free ressources around, just spice them up with a bit of custom art, then it might actually be profitable.