I'm sure I'm late to the original point of the thread, but I'm a big Mamiya 7 fan and user of one. My "real" work this past semester was almost entirely shot with my 7. I started out with the 65, but I shifted to the 80 in August. I haven't looked back since, and the 65 is eventually going to be sold. They're both great lenses, particularly the 80 (which is outrageously sharp).
I got lucky with the original purchase price of my 7, which was $550. The guy I bought it from threw in a lot of film with it, which ended up being an added value of something like $200 (because it was mostly 220 film). The 65 came from KEH, as did the 80. I got the latter for $600 in BGN condition, which I thought was great, until a few days later when a LN- went on sale for $615. Oh well-- my 80 looked new to me and has worked flawlessly.