Surrogate mothers are also human and we should treat them like humans not machines, they're not a thing that you can hire for a while and then forget about them forever.
A wet-nurse has a great status in Islam but do we give them money for breast feeding or after they're done we forget about them completely? No. Look at the Prophet(SAW)'s example with how much respect he treated his wet-nurse, her children were half siblings to the Prophet(SAW). And she only breast fed her for few months.
Imagine a woman who actually keeps a child in her womb and bears it, what do people do to them? Do they give them the status of a family member?
He (SAW) was also able to give her that degree of respect, eventho she did not marry his father. I think individuals CAN go about the relationship in a just, caring, and ethical manner.