If we’re talking solely exploitation of poor women then we have to add sewing in sweatshops to that list. The thing that make prostitution and surrogacy special is the degree of intimacy involved and, at least depending on person, prostitution is closer to sweatshops in that regard than to surrogacy. Not to mention that there’s also a kid involved who didn’t consent to anything at all. Adoption can be traumatic, with surrogacy that’s done with premeditation.

And yes, at least according to German law contracts about sexual services aren’t enforceable from the client side, you’re not entitled to more than your money back. In countries without legal framework the situation is generally way more nasty. And just for completeness’ sake: It’s on the list of jobs the welfare office can’t make you take up.