I just picked up a great condition used Sachs 7-speed as a spare for my ride - paid almost nothing at the community bike co-op. it has the pair of ring seals which double as the bearing holders internally. Really nice looking - I've used Sachs FW before and they shift (friction mode) like any other I've used. My is a 12-13-14-15-17-19-21, but I've seen as high as 28 teeth around. You might want to check ebay.

Update: Was on ebay earlier this evening and they had a Sachs 7-speed just like mine starting at $30.