I own a post-ban too. That price seems a bit high, but these are not common and Colt magazines are hard to locate, so I would start at that price and see if you get any nibbles. (Also, most people I have talked to do not like the 9mm, until they actually shoot them and realize they are fun to shoot.)
Also, what kind of magazines and capacities do you have???? If you have any extra COLT magazines you wish to sell separately, send me a message through AR15.com (IM Button) with the price, condition, capacity, etc.
Thanks.