Polaroid made tons of cameras for these things, some are now available very cheaply and some are kind of expensive. The cheap ones are really cheap and tend to not be the greatest, but some are definitely better than others.
As for the older cameras, the cheaper ones with the 114mm f/8.8 2-element plastic and the better ones with the 114mm f/8.8 3-element glass lenses sell for very similar prices with the possible exception of the 250, 350, and 450 which have Zeiss rangefinders. I got a 240 for $10 plus shipping on eBay. It was in fantastic shape and included the case and user manual. All of the above use funky batteries, but they are still available. What I did was go through what was listed on eBay and then check on the Land List for specifications at http://www.rwhirled.com/landlist/landdcam-pack.htm. Many of the colorpack cameras have 3 element plastic lenses, so the glass lens versions above should be better.
The newer ones tend to sell for too much, such as the ProPack. I actually sold mine for $150 on ebay and bought the afore mentioned 240. I did just check on eBay, and it appears prices have come down some, but I am still happier with the 240 I got than a ProPack for $50. They generally have plastic lenses and are, at a minimum, no better than the above.
The better models sell for a lot. The 180 sells for $300 and up, it seems. For that, there are probably better options like the Mamiya Universal or the Speed Graphic with a Polaroid back. The Polaroid back for the Mamiya RB67 gives a roughly 8cm X 8cm square image that is a lot larger than the 645, but it still leaves a lot of area unexposed.
One other thing, there is some fun Polaroid film available for sale at The Impossible Project at http://shop.the-impossible-project.c...p/film/type100. It is kind of pricy, but they do have some of the Chocolate Polaroid film that they made toward the end. It is expired, but not too badly. Plus, it supports the production of new integral instant films.