its easy to add coolant - there is a kit (a pipe)

and R134a at autozone and you can add the coolant following instruction easily. I did it couple of times.

basically you connect the kit to your car (there is a connection spot along the coolant circulation line)and coolant(sealed at this moment), then start your car, run the air-conditioner, and then drill in the coolant container and let it open. The air-conditioner will suck all the coolant into the system. You will feel the bottle becomes very chill.

It should not be that expensive. Hope this helps.