I think $629.99 is not a bad price including shipping.
http://www.slickguns.com/product/smith-wesson-mp15-sport-556mm-nato-16-barrel-30-rnds-64999-fs
http://www.slickguns.com/product/smith-wesson-mp15-sport-556mm-nato-16-barrel-30-rnds-64999-fs