I have the .22LR/.410 version. I purchased it over 25 years ago, and don't recall what I paid for it, but I believe it was in the $300 range. I don't use it much, it spends most of its time in a safe. It is accurate, but the squeeze/grip type trigger takes some time to get accustomed to. It's nice having the .410, if it was used in a true survival type situation. If I was doing any bush flying, I'd probably take it with me. I know they've gotten expensive, because of their collectability. For me, after having one, I don't think I'd spend more than $400-500. You can buy a couple of takedown 10/22's or AR-7's for a little bit more. They're kind of like the Marlin Camp Carbines, which have become overpriced over the years.
I have some AR-7's and some takedown 10/22's and they're more fun for target shooting. The M-6 is really useful for survival, but that's about it.