I think the general average price is between $600 and $700. That said, it varies widely too. I have seen them sell for as low as $400, often for in the $500s. Some go for $800 or more.
The M2 is a tricky bug to nail down. Yes, condition means a lot, cosmetic and functional. Is the viewfinder clear, showing any delamination? Does it have a quick load kit installed? Button or lever rewind? Self timer?