The gun you are talking about is the M94 Big Bore. It is considerably more expensive and far stronger than a standard M94. The .356 Winchester cartridge operates at 52,000 CUP, which is right there beside a .308 Winchester. Take a look at the extra steel at the back of the receiver and you will see the difference.

If you really want it that is an OK price, but a little on the high side. I have seen them go more for about $325. Ammo availability isn' t that good and it' s usually expensive when you find it ($25 a box or so). However, if you are a handloader Winchester still makes brass for it. It would be best to go ahead and buy about $200 rounds of brass if you decide to get it.