Bathtub faucet replacement

Was trying to repair a very old faucet and seat - lost the parts. Faucet VERY old. Needs replacing now, can't use water until it is. The tile will have to be removed and bathroom butts up to half bath on adjoining wall. This is NOT a diy.job. Faucet and tub older than dirt, installed in mid 50's. Lost one of the faucets. I could order a new seat (did but lost it with the faucet) but replacing the faucet? Is that doable? Live in very isolated area and plumbers are scarce and scattered. Would take 1-2 hrs. to even get here and at their prices I'd have to sell the farm. This HAS TO BE DONE by Sept. 1. I'm heartsick, was trying to do a good thing that backfired on me. (not my house if that tells you anything). Wish it WAS mine, wouldn't feel so bad. I'm desperate. PLEASE - HELP!