I'm struck most by your saying that it is 100 degrees in the room. The only way you're going to get real improvement is to INSULATE at the garage /attic wall. The attic area can easily get to 140 degrees, and all that heat radiates right through to YOU. It is NOT that expensive to do, if this guy told you it is, then you need to get a 2nd opinion & DON'T use that guy ! Insulating is something homeowners can do, other than the new foam expanding insulation. Also, how much insulation is in the exterior wall and ceiling ? More cooling won't help much if the attic / exterior heat is coming through all the time.