Evaporative coolers make an inexpensive solution to cooling in the Denver area, where relative humidities average 67% in the morning and 40% in the evening (source).  As the chart below shows, evaporative coolers make a fair choice for home cooling up to about 90 degrees of temperature for the warmer evening hours, so all but the warmest summer months in Colorado.  Bob's Heating and Air Conditioning recommends an air conditioner to deal with the months of July and August, but we would be happy to sell, install and service your evaporative cooler.