There are many reel to reel machines on eBay, but I think one needs to be cautious as even the best ones, if 25 years or older would almost always need some serious service. Electrolytic capacitors have a finite shelf/use life and trim pots tend to get oxidized to the point where any re-calibration of the playback/record electronics becomes frustrating if not impossible. Having worked for ReVox in the early 1970's I am most familiar with their line of A77 decks and while they were arguably the best home type machines offered at that time and for some years to come, they always need reconditioning to be reliable and capable of performing up to their published specs. If an example presents itself with heads that are evenly and not overly worn, are of the track configuration and speed range you are after and basically works (i.e. can transport tape, no broken knobs, panels, reel hold downs, failed meters), you can expect to spend about $200-$300 for a refurb kit that will replace all electrolytics, tantalum caps, trim pots, motor start capacitors, suppression caps and possibly the three transport relays and some new brake linings. Overhaul takes about 2-3 days depending on your patience and ability. I would be very wary of cheap kits as they often use substandard parts or ones that are even the incorrect values. I have bought some of these A77's on line for relatively cheap prices and have overhauled a number of them with good success.
I've done a lot of location recording over the years with A77's, A700, Tandberg 10X and Nagras. My current flagship RTR is a Studer-ReVox PR99MkIII. Location recording at my advancing state of decrepitude using heavy open reel machines is pretty much out of the question. In the field, I currently use a small digital recorder and have been quite satisfied with the results. No wow and flutter, no tape hiss, conservative record levels, no audible (to my ears) distortion and no mechanical noise which allows me to sit in the audience and actually watch the performance. An added benefit is that I never run out of tape, something that at 15 ips happens more often than you think.
That said, if you HAVE tapes and want to be able to play them, obtaining a machine and maybe having it overhauled might be worthwhile. If you just want to have the joy of watching the reels spin, that might be reason enough to buy one as well. If you have deep enough pockets to buy new dubs of masters at $300-$600 each, and are willing to live with the limited choice of program material, you will need a 15 ips 1/2 track machine and a good one can be expensive. If you don't care about portability and have and extra $5000 plus shipping, you can buy a beautifully reconditioned MCI JH110 from Mara Machines in Nashville. Be aware though, that studio machines do generate mechanical noise that might make having them in your listening room intolerable.