Help with buying air conditioning units?

We are looking to buy a new air conditioning unit, with everything included. We want the outdoor unit, and the coil, and whatever else comes for the inside as well. We are not really well prepared to shop right now, and any help is appreciated. The guy that might install the unit for us is asking for $3200 with the unit and his labor. The unit is a 3.5 ton 14 seer air conditioning unit. I don't know if this is a good price or not. Also, is there any where that we can buy a unit ourselves, so that we can just do that and just pay for someone else's labor? Any and all help is really appreciated. Prices, and personal experience with the matter is definitely encouraged.