For what it will cost to hire an editor to do any amount of real editing on a book, I would think the money would be better spent taking a college-level course on plot development, technique, creative writing, etc.
The only reason someone would hire an editor is if grammar, plot development, etc. is difficult or a lacking skill. And even if an editor is paid a lot of money to work over a piece, it doesn’t guarantee it will be accepted anywhere. Plus, if the piece is accepted, then what’s going to happen when the agent or editor calls and needs a chapter rewritten ASAP? Then it’s up a creek without a paddle.
So, I’d spend the money learning how to edit my own work.