SadieKate,
I went to a Sportsmedicine/PT place called Champion Sports here in Denver. I wear them for a foot problem and chrondolamicia in the knees.
I've had them made by physical therapist and pedothists (people trained to specifically make orthotics) but in my case the pt's do a better job.
The initial pair were about $250 which included the evaluation . The ski boots and cycling shoes were less, $150 per pair.
You can also go to a podiatrist, but the podiatrist I consulted couldn't diagnose my foot problem. I had to see an orthopedic foot specialist to find out what was wrong.