I've had a basic valve job done for $125, it included hot tanking, freeze plug replacement, valve and valve seat machining, new valve seals, testing valve spring pressure, and machining the surface to make sure it was flat.
If the valve guides require knurling or replacement there is an additional charge.
If you want it done cheaper, and help some students along the way, a high school auto shop will perform a valve job for almost nothing ($5 per head, plus parts when I was a student). My class used to do them frequently. Turnaround time isn't as fast as a pro shop, but the work is inspected by the teacher before being let go.