Big ones are expensive, but that seems a little crazy to me. I paid $4/each for mine at Petsmart at one of their 50% off sales. They were only 2.5" at the time.
I am no expert, but I have seen 5" ones at online stores for about $30.
Small clown loaches are cheap, I consider them "community" fish. However, 7"+ clown loaches are "monster" fish, and I'm always looking to purchase them.
From my experiences, locally and MFK Socal:
7-8" - $100 ballpark
8-9" - $100+
10"+ - Never seen for sale
12"+ - Priceless (check out the SF Academy of Sciences cafeteria, enjoy a great Bar b Q pork bun while you are drooling over the fish!)
Basically, if you really like large clown loaches, buy them big. You'll be an "old" man before they reach 8"+!
That seems a bit steep if you ask me. I go to my LFS and find trade-ins once in a while. In fact I found a beautiful 6" CL and picked him up for $10 (Yes, I understand that's an unheard of price). They should be willing to come down in price some.