A family member had great luck with Meridian Valley Labs. You can order a parasite only culture, or a CSDA. The test found Ecoli, low lactobaccillus, and no parasites, pretty fair assessment of her condition. They sell a parasite culture for around $100-125, a Giardia antigen for something like $50, or a CSDA for a little over $200.
A parasite culture is a $30 test through Lab One, so it shows what types of profits some of these people make. But if you want the test w/o going through a doc, it's an option, I guess.