Deck mounted faucet replacing cost.
I'm not a plumber and I don't write bids but I did install my own roman tub filler.
Look at the price of Kohler roman tub fillers at a big box store and you will see that the cheap ones are at least $200 and that doesn't include the valves which will cost you another $100. So, for faucet material alone, you are already over $300 and that is for the cheaper end of the faucets.
It looks like you will also have drywall costs, paint costs, and then the time it takes for the plumber to complete the job. If he has to repair drywall, it might take more than one trip because he has to wait for the mud to dry between coats.
Why don't you try it yourself? It isn't that hard.