Let's put it this way. Right now, they are of similar value (dependent, of course, on the condition). But in a year from now, the D80 will be worth much less than the M2. Of course, you probably need to spend at least $200 more, and possibly as much as $400-$500 more for each lens that you will want for the M2. About the cheapest decent lens you could get for the M2 might be an LTM mount lens, which would need a $20-40 adapter to fit an M2. A good inexpensive choice would be a 50mm f2 Summitar, or any number of fine nearly new Voightlander LTM mount lenses.
But I gotta tell you, I personally sold almost all of my Leica-mount gear last year, and I haven't looked back. All I kept was a Bessa-T with a turret finder, and a 50mm Summitar. It's an amazingly retro outfit. Gone were the CLE, the Hexar RF, the Bessa-L, and a half dozen M-mount and LTM mount lenses. Pretty much the only film I shoot nowadays is medium format. But I kept the Konica Auto S2. It's 80% of the camera that a Leica M2 + a Summicron is, for roughly 5% of the cost.