If it the coil spring air bag. I bought mine online and went to a local truck repair shop (I try to avoid RV places for any Chassis problems.) where they installed them for less than $100.00. The bags were right around $125.00 delivered.
That being said some people have had luck cutting out the old bags and pushing the new bags up through the bottom of the coil spring. That did not work on mine and the arm had to be removed. I was lucky as I have a really good truck repair shop and they allowed me to buy new shocks and brake pads which they installed when replacing the bags. They had to take the shocks half way off and remove the rotors in order to drop the arm.
Try to find a good independent truck repair shop and go there for all your service needs you will be a much happier person and their rates are much less expensive than an RV place
Looking through your area I see Hargis trucking and repair and Poor Boys I would give one or both of them a call or go by their place and talk to them