Apparently another company is trying to compete head-to-head against Window World:
Denver Post Ad for Clear Choice
Careful, service companies like this always try to upsell you on anything they can. Stick to your guns if price is the most important thing to you.
In order to get windows that qualify for the Energy Star rebate, expect to pay significantly more than the $185 shown in this ad. Even if that eats up the whole rebate, remember you should save money every month because you will have a better window that loses less heat.