New member introduction, questions on HP 21XX series machines, reliability and maintainability

I just joined the list. I've had a long-time interest in old computers, and rescued a "straight-8" many years ago when I didn't think anyone else thought of it as anything more than junk. It was at least minimally operable when I obtained it, but I went off to graduate school before I could find any software for it, and it's been in storage at my father's office in Florida for ~15 years now. I hope to move it to my current location in the next few months after a family visit, but in the meantime, I'm looking to acquire another minicomputer from the core memory era, hopefully something slightly more compactly packaged than the (presently rackless) rack-mount "8".

After some research, I have settled on the HP21xx line as a good candidate. These seem to be very nice, well-built machines with a reasonable architecture, a good paper-tape BASIC, and a full complement of "blinkenlights". It seems that these machines are actually still used, however, and I've been quoted some pretty steep prices from a nearby dealer in in used HP gear.

I'd be interested in comments and advice for a prospective 21xx owner from those on the list who own these machines or have used them. I'm particularly concerned about reliability, since at the price I expect to pay, I want to keep it operating for a long time to come. How difficult and expensive are they to troubleshoot and keep working (say, compared to DEC PDP-8)? How available are contemporary replacements and/or new old stock for the ICs? Are there any proprietary components that are particularly prone to failure or hard to replace that I absolutely must obtain up-front as spares? What about the core stacks themselves? The dealer that I talked to seemed to think these were problematic (though I did not speak with his technicians), while my instinct would be that the core itself (not the driver electronics) would be among the most reliable and stable components, barring visible corrosion damage.

Also, any suggestions on places to look for these machines on the cheap would be welcomed. What I'm most looking for is a 2115, but would likely be interested in the somewhat later 2100 as well.