Need to do Top End on my 0200A Continental Engine

Due to low pressure in 2 cylinders my mechanic says it's time for an overhaul.
The engine is 40 yrs old and only has 680 hrs TT as it was stored for 20 yrs.
I've been flying 50 or so hrs for the past 8yrs and the engine runs fine. It
appears that the rings are worn but also some of the leakage may be from the
exhaust valves. Question. I plan to take all cylinders/pistons to an overhaul
shop for complete overhaul. What usually is a typical scenario for work done:
cylinder bore or not, new valves or not, valve guide work or not? What is a
typical cost for the shop work per cylinder? I am hoping to keep the costs down
and don't like surprises. Thanks

Larry/San Diego