Bridgeports & clones might be the best deal factoring price and function. I see Bridgeports selling for the low 2,000's at auction. Most hobbyists just do not have the space required, which is why a Clausing sells for a similar price.
I don't know the actual numbers but based on what I see on the used markets there must be at least a 10-1 difference in the availability of BP and clones vs smaller mills like the Clausing, Rockwell and the similar size imports. I'm being very conservative on that number, and wouldn't be surprised if it is more like 20-1. Even adding in some the the mid-size mills like the Mill-Rite, or older (and smaller) M head Bridgeports don't increase the availability of "smaller than a BP" mills by much.
Issue with many of the larger mills like a Bridgeport is height as much as floor space, at about 8 feet tall a lot of older garages and basement shops lack the ceiling height needed.
As far as tooling goes, I do see deals on well tooled lathes, but this seems to be much less common to see with mills. I think this is because mill tooling is more size based, not machine based where a lot of lathe tooling is very size dependent and often machine specific.
If somebody buys a new mill, a lot of the old tooling can move right over to the new mill. Even if you bought a bigger mill a lot of the smaller mills tooling could be useful until replaced or in addition to the bigger mill tooling.
If you replace something like a SB9 with a new PM 12x36 there is not much tooling from the old lathe you would want to keep, so might as well throw it in with the lathe and push the price a little higher.
