I've only done spot wet sanding.
I wouldn't pick up a job where I would have to wetsand a whole car. Not me!
That said, and somebody correct me if I'm wrong, the going price -depend on where you live- for wetsanding is about $75-80 per panel to for what I've heard in some detailing forums.
Of course there are variables involved, such as th finish sought by the customer. Does he want a completely flat, OP free finish, or does he just want to remove some defects?

Anyway, I've had people come to me to do a whole wetsanding job, and I've turned them down.
For one, I'm not a body work man. I can do small spots and small panels, but taking up on a wholw car is just putting myself in a situation I don't want to be.