Greetings Jason:
Don't be in any hurry to sell your timber without receiving an unbiased assessment from an independent consulting forester (i.e., someone who can independently appraise the trees apart from the consulting forester who initially appraised your timber seeing as your original forester has NOW become a prospective buyer of your timber).
M/M means price per thousand board feet. What the forester meant to write is $1.5M/M (i.e., $1500 per thousand board feet = $1.50 per board foot). It is more common to use $/MBF or $/bf.
The easiest solution is to contact a different, but independent consulting forester to assess the value of the trees that the original forester is wishing to purchase. I would then market these trees to several perspective buyers to avoid the pitfalls of selling to one buyer who ultimately may or may not be the eventual winning bidder of your standing timber. This, of course, is what we refer to as the basics of timber marketing. This is my recommendation because you are now encroaching upon a conflict of interest--your independent consulting forester is now wanting to buy some of your timber. To avoid this conflict, get another independent consulting forester involved!
Best of luck!