I don't think there is really a good/bad market for the M7, they are already a niche. Price it to sell and someone will buy it. Check gunbroker or the like to get a sense of what they are going for. There are many variations of the M7, some are worth more than others. The action can easily be rebarreled to many different chamberings, but IMO most people that are going to go that far, will just spend the same money on a new rifle, mostly likely as light or lighter.
Not knowing what configuration your M7 is, it could be worth $400-maybe $700. I've been shopping them for a few months looking for a 223 or 204. Not a ton listed compared to other makes, but again, not a huge market for them either, I don't think.