Plumbing-Shower (hot water) knob leaks. How much will it cost to fix it?

I have a house that I am renting in NC and I live in CA. The hot water faucet in the bath shower is leaking. I need to get someone to fix it. What needs to be done and how much should I expect to spend? My tenants just moved in and I want to solve it for them asap without breaking the bank. Thank you so much.