The RobArms website shows the former MSRP was $600 (currently $550, but Out of Stock) and MSRP on the brake is $50, so that dealer is pretty much asking MSRP at $650. Since NIB VEPRs in 7.62 are pretty hard to find right now, the dealer seems to be pricing for demand/supply.
My -K in .223 has a brake, and it does a great job keeping the barrel under control.
VEPRs have a non-standard one-piece foregrip (no front grip plate, only a single-screw barrel attachment point) and the receiver has an angle cut which is also non-standard (a sharper angle than an angle-cut MAK). Owners who have done stock conversions have had to fabricate their own rear receiver fill plates to straighten out the cut (the sharp cut leaves almost no receiver metal for a standard AK PG to rest against) and their own or modified ACE receiver blocks to form attachment points for non-wood stocks, mostly ACE or AR-15 style skeletons. VEPRs have the RPK-style receiver with the heavier 1.5mm metal and the reinforced front trunion, and RobArms has carried through by installing its own RPK-style stock, which BTW has a one-piece stock/PG which solves the issue of the lack of receiver metal for the PG to rest against.
Just a guess, but they may be doing all this to minimize 922r issues with the BATF by ensuring that standard AK parts are not easily substituted.