why did it cost so much to place my blower motor

I believe you looked up an estimate for a blower motor resistor, not the actual blower motor. Check out the estimate for the blower motor and you'll see you were charged fairly: https://repairpal.com/estimator/nissan/pathfinder Also, diagnostic charges are a necessity before replacing a part, you have to verify what the problem is before replacing parts, and that's to your benefit. (unless you can demonstrate that you verified the blower motor had power and ground to the blower motor and it wasn't working)

Why is gas at Exxon 2.79/gal. and at Hess it's 2.59/gal. People and company's can charge what they want. Please tell me you didn't expect Firestone to fix it on an estimate given by a web site not even affiliated with them. Because if you expected any shop to honor someone else's estimate you are really in the wrong ball park. Why didn't you get an estimate from Firestone? Did you just figure the repairpal estimate was "law" and tell Firestone to so the job? Sorry that aint the way the world works.