Shut off valves or angle stops- standard charge $50. each.
Try using a channel lock plier and turn the handle with it- Clock wise and loosen the rust inside first. If that don’t work, than call the plumber. stardard charge- plumber- $100. DIY- Free. The valve is only used when u need to turn off water for that faucet- so if it don’t drip water, u don’t need to replace it.
Keep that $100- $150. and try what I mentioned first.

replacing the valves is not the expensive part, its very easy. However most plumbers have a minimum charge or only charge by the hour, so it can get expensive that way. Highway robbery I know but don’t blame the guy who comes to your house, its his greedy boss that is to blame. Try phoning the service plumbers in the back of the phone book and compare quotes. We might be talking about 60-100 dollars here.