IF it was pre-ban it MIGHT command a small premium over a brand new post ban, but not much. I mean, the only difference is the bayonet lug which doesn't make the rifle look silly like the naked barrel of a post ban AR.
Given the ratty condition, I'd take a closer look at it. If you have a friend that is into high power service rifle competition, take him along to look it over. It just might be well used in competition as I have seen several M1As that were borderline eyesores with enough work on them to make them a bargain at that price.
Look at the rear sight and see if it is standard (stamped apeture) or hooded (cone style). Inspect the front sight and see if it is mil-spec. or NM. You also might want to take the trigger group out and look for aftermarket work (i.e. hammer lightening, ect.) Also look to see if the stock / receiver is glass-bedded.
If it doesn't have alot of NM parts on it, you can assume that the shop probably stole it from some guy on a trade in on something he had to have. I wouldn't be surprised if they only had around $500-$550 in it if that at all. Hell, they can't have too much in it or else they would have probably spent $100 to refinish the thing relying on the bigger bump in value of a pre-ban in premium condition.
If it isn't even a pre-ban rifle RUN DON'T WALK AWAY. Remember, its for the children.....
Saleen