IMO, disregarding wear and damage, there is a quality difference between the old Bridgeports made in the states and the new imported ones that are IMO the same as any other Taiwan knee mill. Not to split hairs or anything, but IMO if you are weighing costs, I'd give more value to a proper rebuild over a new import. Not to say all imports are poor quality either, it just depends where you want to put your money. Also consider that by the time most guys are looking at rebuilding a mill, it already paid for itself a long time ago, so the cost of the rebuild IS the cost of the machine.
If you are like the rest of us who don't have money to blow on the "good stuff," the usual routine is try to find something used but better than what you have, and if you need better you rebuild it yourself. With the exception of buying parts, most of the cost of a rebuild is in hours spent disassembling, cleaning, finishing, grinding, scraping, inspecting, assembling testing, etc. It's of course a big learning curve and not everyone has the desire or resources to get into refitting knee mills (especially if it's a one time gig), but most of us already have the tools a skills to do a good "paint job" rebuild, making it look nice again and getting mechanical things set right, so from there you learn how to measure what is worn and how much needs to cut from where to make things flat and geometric again, price out sending individual pieces for plaining or more often grinding for the bulk of your material removal, then you do the final scraping and assembly yourself. There's risks and no warranty, but it seems to be the most common alternative to replacing your ol' iron with new imported stuff.