I have an M6 in .22LR/.410 and I quite like it. I purchased it on EE a few years back for $850 (I really wanted it). Since then, I've seen less than 6 come up for sale here and on #######. It doesn't come up frequently. I've only seen one in stainless come up and I think that was at auction. Hard to say what they actually sell for, I find the higher prices basic M6s sit for a longer time. If you had the blue case, or a scope it sells faster. Based on the above I'd put the value on a Stainless Springfield M6 made by CZ between $1000-$1200. That said, you'd have to find the right buyer. For that kind of money the TPS M6 looks pretty good. This is more of a collector's price.
I might pay a premium for one with a blue case, and more still for one with a blue case and the M6 scope: but I'm not very smart.