Bill Ross writes:

Are old mills on the market for $2,500 likely to be worn out?

Very likely at that price.

My Bridgeport Series 1 price survey has been: $1500 for serviceable but
with severe wear or broken head, $2500 for running but with moderate to
severe wear, and $3500 and up for running with light to moderate wear.

How much is it going to cost to get them into good running shape?

I am now working myself on scraping a well-worn (e.g., middle of knee
concave by 0.005", gibs shimmed with pieces of crate strapping metal!)
Bridgeport. It has been quite educational and a project of making tools
and gages in itself. Quite a few $100s in cash to buy books and tools,
and quite a few hours making and improvising some of the tools. Getting
this kind of rebuild done right is perhaps $3000 to hire out, and you
probably have to ship the machine to get it in the hands of someone who
does it. I figured out why some of these old machines have such pretty
body-shop repaint jobs on them: the effort to do that is a small
fraction of the effort to get the machine back to factory alignment.

The most valuable lessons of all are that I am now become knowledgeable
at evaluating all aspects of Bridgeport wear. There's no way you can
work on repairing alignment without knowing everything there is to know
about measuring it first. Sometimes you learn the hard way. I spent a
week rough and finish scraping the knee ways, and then discovered my
datum surface was off.

I am also converting the ways to teflon bearings, which should make this
machine last forever before realignment is needed again.