I wouldn't even start if it was "free" unless it didn't really NEED much, and I was certain of that.
Unless you do this as a routine biz, one after another, you are bound to end up spending more than an "already decent" BP - or the work-alike equivalent, some other brand-name - even at what at first seems to be a "premium" price.
Long and short of it is that CNC took over most "for revenue" milling long ago, and all sorts of light/medium all-manual mills got shoved aside first, then out the door, second.
By now, as with '57 Chevy Bel-Aire's or early Mustangs, nearly any other less-popular make goes cheaper utility-value for money-cost than a BP.
Some of those "unpopular" models don't even have much wear on them.
BP does have the advantage that just about ANY part can be had from "somewhere", even if a reproduction.
If you NEED one to earn a crust, far better to pony-up the price of a known-good one.
If you just need a "project"? Hard to give advice.