Leica and Nikon optics are maybe equally good, if the Leitz optics are not better.
Rangefinders are a different world compared to SLRs, I'd advice you to go to a photo-store and "feel" one.

Yes, you can find an M body for under $2000, look in the used section of KEH, B&H, Adorama. Or you can get a Voigtlander Bessa