Major Tom
Established
You can pretty much bet you can get back what you paid for if you get a Leica. You can resell it and maybe be out the shipping. They hold their value. You might even make a little. I found a deal on a Mamiya 7. I shot it for a year and sold it for more than I had in it film and all.
By the time I am old and retired I imagine the value of a working M3 or a Barnack/Barnack copy in good condition will be rather ridiculous, just as collector items, not cameras.
It begs the question of whether film will still be around, besides old stock.