Orthotics can be worth every penny. However, let me warn you against getting orthotics through any source other than through a referral from your orthopedic doctor. I ordered them through my podiatrist last year (after I let him perform a surgery I should not have), they were made by some company in WA (I'm in KY), they did no good at all and it was a hassle to try to have them adjusted. So I went to an orthopedic surgeon and he referred me to a clinic in town where they make prosthetics as well as shoe orthotics. They are made on sight and they can adjust it right then and there until they get it right. It has made a world of difference!
I would be very hesitant to spend that much money on something at a retail store rather than a place where my medical doctor sent me!! That being said, my insurance fully covered mine last year, but this year I had to pay for them at the discounted insurance rate of $318. Before shelling out the money, see an orthopedic doctor that specializes in foot/ankle (do not waste your time with a podiatrist if he is in serious pain).
Edited to Add:
I have nothing against podiatrists in general. They can treat some minor foot problems effectively. However, podiatrists are legally held to a different standard than orthopedic medical doctors, and therefore there are significant differences in recommended treatments between the two specialists. If a podiatrist ever recommends surgery, seek a second opinion from an orthopedic surgeon to avoid my mistakes!