Less than 1500 were manufactured, the exact number is unknown
Smith and Wesson did not heavily push the 357SIG cartridge, after all it was in competition with the 40S&W for market share
I am a huge fan of the 357SIG cartridge and have 3 SIGMA SW357Vs among my 357SIGs at the moment
SIGMAs, in general, are not well liked in many circles and do not have great resale value. There are what they are. good and reliable duty guns. They are not plinkers or target pistols and can not be modified into such
Yours is a shooter, not a pistol in collectible condition. It will probably bring a premium over other calibers to a fan of the 357SIG, but probably nor more than 20% or so.
I would think it would bring $350+ without too much trouble.
BTW, street price on SIGMAs (with two 15 round magazines) when they were released just prior to the 1994 Crime and Control Bill (AWB) was over $600.