TOTALLY AGREE! This is the only way to get good efficiency. Only a licensed contractor can legally handle the refrigerant and the fines are pretty steep if you get caught. A good one will be able to do the HL calcs, advise you on warranties and SEER, etc.
The price ranges you are seeing are related to SEER rating and the compressor quality. The higher the SEER, the higher the price and the less it will cost to run. I like the total package that the Amana units provide. SEER, ability to clean and not damage the fins, longevity are all considerations. An improperly sized unit on the cheap will end up costing you more than doing it right the first time.
Swamps in Colorado do work reasonably well due to the low humidity, but they do have other issues, especially if you or another resident have any respiratory issues or allergies. You can usually get a dT of about 20F, so when it is 100 out, you will be at 80, but most of the time, not bad. Personally, I will take AC over SC everytime. I pulled the SC and put in AC at my first house and the power bills were maybe $20 more in the summer, 1200SF with a basement.