At Avian Biotech, the cost is $19.50 for a test using blood samples or 24.50 for a test using fresh plucked feathers.....either test is you providing the samples, ABI will provide you with free sample collection kits.....
But that's British Pounds, so roughly $30? Avian Biotech seems to be most peoples favourite firm to use for it though. If you can't stand the idea of stealing some blood or pulling feathers, ask your vet or breeder, they're usually more than happy to do it