What Is a good website to buy a used diesel truck In the western area? (I live In utah)?

I am looking to buy a Diesel 4 dr 4x4 longbed with preferrably under 100,000 miles (50k or less would be best), no fords unless it was the best deal on the planet. I want either a Duramax or a cummins a 2005 to new. I have been looking on ksl classifieds for months but not much luck so If anyone knows a good place to look or has a truck to sell, I would appreciate it if you would tell me. My price range Is $15,000 to around $30,000 but if its 30,000 It better have way low miles and be In Immaculate condition, I do not want to buy from a dealer and be ripped off.