I've just re-bought a 1965 IIa that I owned 4 years ago -- yes, that is a good demonstration of how these trucks will get under your skin.
I can tell you, you will never, ever, ever find one that will not need work. Mine is in good shape, everything works, but when everything works, everything seems to leak more.
I can also tell you to largely ignore paint, anyone can put a fresh coat of paint on one of these and make it look good. The best ones will have no rust, little corrosion, and they will have a long list of rebuilt or new parts. A Series III is the best, but they don't really look as good as the IIa -- in my opinion.
In this current market you can expect to pay about $5k for an 88" that is good, running, fixable. You can expect to pay $7+k for a 109" that is good and usable. At those prices you will have things to fix. If you go higher than that you can expect to have something that runs very well, rattles a little less than the others, leaks oil, and you will have to do work on it within six months.
That's not to say these aren't actually fairly reliable trucks, or that they are particularly fragile. Think of how old they are! Mine is an original truck, with a few bits replaced or rebuilt, and it's been driving the past three days with no alternator, headlights on and everything -- will your DII last that long?
There is a good 109 for sale in Washington, check the Craig's List ads in that state.