"...Demand. Scarcity..." Yep. Far fewer sniper variants were built. Far more than twice the price too. Depending on the rifle and in some cases, what comes with it. Not all sniper rifles were issued in a box like No. 4 Mk I T's were.
There are a lot of fakes out there as well. Scoping any milsurp, even with a vintage scope, doesn't make it a sniper variant.
Mind you, you don't need an RPAL for one.