$120 to evac and recharge is dirt cheap. I used to love a/c service, I'd make 2.6 hrs just to hook up a machine and let it do all the work, good times.
You're going to have to hook up a set of manifold gauges to see what is going on with your a/c system, or take it to a shop. A good rule of thumb is whatever the pressure is on the low side is what the temp the a/c system should be blowing (36 psi on the low side roughly equates to 36 degrees out the vents, etc.). If you know for a fact your system is full then it is mostlikely the compressor or the expansion valve.