Initial inspection is always FREE. It consists of removing a few valves and giving the head a once over. We can usually tell if the heads are prepared properly. At that point we will advise maintenance, further inspection, poor preparation, not right for your combination, or OK to use.
Further inspection would be completely disassembling and cleaning the heads. Check guides for condition and stem clearance. Check valve springs for tension. Check the fit of the retainer in the spring and the fit of the spring in the spring cup, locator, or spring seat. A visual inspection of the valve seat/valve job, possibly lightly lapping the seats. Note: lapping is nothing more than lightly grinding. Over lapping can cause unnecessary wear to your valves and seats.
We cannot "quote" a price on further inspection. It depends on how much cleaning is necessary and how much time it takes to disassemble your heads. It is a time and material charge.