rei.com outlet section has good pricing but the size and selection may be picked over. blueskycycling.com, pricepoint.com, huckandroll.com all carry good shorts.

I also use spandex under a pair of cargo shorts most of the time. Costco has good cheap cargo shorts this time of year. Investing is a good spandex short with a quality pad is a smart buy, don't get too cheap there.