Lithium batteries weigh very little. I'm still on a set of Lithium AAs that I put in my Pentax 645NII over a year ago, I'd say at least 70 rolls of film during that time. Many of the lenses can be had fairly inexpensively although the 645D digital camera has kept the prices of the autofocus ones fairly high. It's the best camera system I've ever used and the one I'd stick with if I had to keep only one.
Originally Posted by trythis
As others have mentioned it is hard to beat the Mamiya M645 if you are looking for a bargain. I had one for a while and it's a cool camera. I sold my entire system with multiple lenses (including the coveted 80mm f1.9), two finders, two film inserts and a whole pile of other accessories for less than $500. Keh prices are low and you can get much lower on eBay.