For what its worth, I just saw a used Ultra Fluted 223 for $299 with the black "dragunov" style stock. I had a Ultra Fluted 223 about a year ago, and I parted it out here. I think I paid around $290 for a special order. The F23 is the most expensive accesory barrel, so don't worry about resale. The stock is nice and ergonomic for prone shooting, and the sliding T- rail for a bipod is nice for adjusting gun positions. The buttstock should also have 2 removable half inch blocks on the back to adjust length of pull. There are shorter screws hidden in behind the last block in case you remove one or two.
See if you can find ANYTHING wrong with it and talk him down at least 10 bucks.