2000 Chevy S-10 Low compression/ Exhuast valve

What you should expect from a valve job.
You can expect the valve guides to have close tolerances with the valve stems.
You can expect the valve stem height to be correct for the spring seat.
You can expect acceptable spring pressure.
You can expect the valve to seal against the seat.

What I will cost will depend on what they have to do.
Will the guides need to be replaced or just reamed?
Will any seats need to be replaced?
Will any valves need to be replaced?

Are you pulling the heads yourself, or are you taking the truck to a shop?

Also find out what kind of work the shop does.
For example find out do they "knurl" the old guides, this procedure will meet specs but will only last 5000mi or so.I would make sure they press the old ones out and press new ones in.
I would go with new bronze guides and stainless steel coated valves with the proper valve seat to match the valves to take the heat. (Especially important on the exhaust valves!). New springs wouldnt hurt anything either.
It might sound expensive but these parts individually are not. I dont know if I can advertise but D&Mauto has these parts reasonably.
New guides, valves, seats! Though you wont gain much hp with new valve train parts, the right parts plus the right job equals good reliabilty.