ARFCOM injects the aids into links so I didn't click on yours.
A NXS 2.5-10x24 with zero stop ran about $1360 new.
They are wonderfully compact and light scopes. You could use one and have a MRDS on it for about the same weight as a Elcan Specter DR.
Very tight and unforgiving eye box, but if you are used to a 4x ACOG, you can handle this scope.
Because they were used by various military units, most notably the SEALs, on a variety of guns they are also desired by collectors. There are also ARMY, RECON, and NAV-SPEC contact overrun models out there that will also demand a premium.
I don't really think they are rare, if you want one, there are plenty to be found. But you are going to pay a premium because there is more demand that supply.
I've seen them sell for up to $3000.