54 of them were shipped to the Marines in 2006, after DARPA testing. The XM-3 was the first precision weapon the Marines had that was both night vision and suppression capable, not to mention that IBA also cut some of the gun's weight. The receiver is not one that was rebuilt from an M40, as I noted above, they are all in the S653xxxx range (the 54 USMC rifles are not sequentially serial numbered). It is "valuable" and "expensive" because some of these rifles are still in use by Scout Snipers, it has exceptional provenance from the CMP (and the gun's logbook), a look at the rifles's logbook could also document and prove recent combat use, and it is the only precision weapon system that is contemporary to the current wars that has been offered for sale by the government to citizens. Those reasons are what makes this rifle extremely rare, valuable and highly collectible. Can wait to see what it goes for!