Actually, after I re-read this, I think some clarification is needed.
I have a "no-ban" SA M7 "R", but the receiver is marked SA M7 "S".
$598.00 for that is a steal.
If it's a post ban SA M7 S with the permanently attached muzzle brake, then $598.00 is about $75-100 less than I paid for a new one.
Hope this clarifies things. (In other words--you may not have missed out on a huge bargain if it's the post-ban one.)