Tire mounting prices tend to vary all over the place. Generally, bike dealers will be the highest (for tires too, but no surprise), but they will take the wheels off for you. Next will be independent repair shops who can also take the tires off. Least expensive will be independents where you bring the wheels in off the bike. There's one shop around here that will mount tires for free if you bring in the wheels and buy the tires from them. Their tire prices are a little higher, however. The two shops I usually go to charge $10 or $12.50 for mounting and balancing if you bring in the wheels. Most shops also charge more if you don't buy the tires from them (also no surprise). It really pays to compare the TOTAL cost of tires and mounting.
BTW, I was talking to my brother-in-law a few weeks ago who owns a GoodYear shop in the Phoenix area somewhere (Mesa?). I was trying to convince him to sell and install m/c tires in addition to cage tires as I thought there would be enough business to make it worth his while. He mentioned three things that I thought were interesting:
There are some GoodYear shops in his area that do sell bike tires in addition to cage tires.
Business is expremely local. His customers come from the immediate local area of this shop mainly (many GoodYear shops in the area?).
And he checked into insurance for doing bike tires. It is WAY more expensive (like thousands per month more) if he were to take the wheels off the bike. This is why shops that will do charge more and why shops that do general repairs are more likely to be willing to take the wheels off for you.