if you live in thornton, WHAC is a good place to go. we just joined it couple weeks ago. it's only 30mins or so from thornton. http://www.wildlifehunters.com/

we have not been to other ranges in/around denver. but for the price and distance, WHAC is a simple choice. they also have regular events/matches free to member and public. cy is a great guy to deal with.