Just to help you narrow things down:
The Clausing 8520 / 8530, Rockwell 21-100 and the import 6x26" mills are generally considered 1/2 Bridgeports and are about the smallest knee mills available. They weigh in around 600-750lbs and are fairly easy to break down into handy size components for moving. Height runs right about 6 foot for most of these. Much less common but another mill in this general size class is the Rotex, a small vintage USA vertical / horizontal mill from the 1950s. The two I've seen for sale were a bargain at about 1/3 what most want for a Clausing or Rockwell. Rotex was a small California company though so the odds of you finding one in Virginia is probably pretty slim, but you never know.
The Burke / Powermatic Millrite and some of the import "mini-Bridgeport" mills are closer to actual 3/4 Bridgeport in size and are significantly heavier than the first group. I believe the Millrite weighs around 1200-1400lbs, there are a couple different table sizes which will effect the final size / weight. These seem to run 6-1/2 to near 7 feet in height vs the near 8 foot of a Bridgeport. The older M-head round ram Bridgeports also fall into this general size being smaller than the later J head dovetail mills.
The import 8x30 is basically an improved and slightly enlarged 6x26 (so a 5/8 Bridgeport?
). These also weigh about 150-200lbs more than the smaller mills.
There is an amazing variety of Taiwanese 1/2 - 3/4 size mills that were imported in the 80s under a variety of names. Some literally look like a scaled down Bridgeport, others look similar to the Rockwell mills or the current batch of Chinese 6x26 / 8x30 mills. If you can find one of these in good shape they often seem to sell for much less than the Rockwell or Clausing mills because people don't know what they are. Parts could be an issue though.
If it helps for figuring out your space I have a Clausing 8520. It fits into a space roughly 3x4 feet, but that is tight, 3x5 would be more comfortable. Something else to consider with a mill though is that they don't occupy all of that space full time like a lathe does, in fact most of the needed space is a couple feet above the ground (the table). You have to leave room for the table travel, but if you are the only one using the shop you can often get away with some overlap. There is also often room around the base below the table where you can keep things that don't mind a few chips. Material storage, tooling cart, covered shop vac etc.
If you find that even the Clausing and Rockwell mills are too big, there are several smaller horizontal mills that can be fitted with a vertical head. Conversions for Bridgeport M heads were common. The M heads are also fairly cheap, I've seen the head only in usable condition for $400-500. I have a small Diamond 5x20 horizontal mill which sits next to my Clausing. Burke, Hardinge and a few others made similar size mills, and at the bottom end of the size scale you have the Benchmaster and Atlas mills which are horizontals or horizontal / vertical mills depending on model and options.
Yeah, I did some homework looking for the biggest mill that I could squeeze into my small shop. I got lucky and was starting to get serious about shopping when someone I know was getting ready to sell their Clausing after buying a Bridgeport.
I'll see what I can do! (After a tidy, of course)
