This is a difficult question to answer. There are so many aspects to consider, not the least of which is the fact that with projectors, the proof of the pudding is in the tasting. In other words, it's not all about specs. You have to see the projector.
You mentioned Runco, and it has an extensive product line for customers on a budget as well as those who manage to do without. Within their line, in side-by-side comparisons, one can certainly see the increased picture quality and brightness capabilities as one moves up in price.
Runco optimizes and calibrates their products for HT use, and you can see the value of that in the color accuracy and brightness uniformity. They also offer turn-key solutions for Cinemascope widescreen enthusiasts including features such as convenient automatic aspect ratio recognition which is available now, as well as a mode for correctly displaying subtitles, menus, station logos, and news/sports tickers at the bottom and sides of the screen. Why would you want to see a station logo, you might ask? You don't, but seeing part of one cut off on your screen is even more annoying.
But it's hard to say whether to recommend and older Runco projector since you don't say which Runco you are considering. Five years is a long time in the projector worlld.
You're right though that there are some extraordinary deals out there. I've seen used Runcos being sold for less than the resale value of the included top line Cinemscope lens. You can do very, very well. The problem is that if your budget is truly tight and something goes wrong with your older $75K or $100K Runco, you won't be able to afford the potential repair. On the other hand, tthe JVC RS45 is an entry level projector, so without a warranty, it won't take much going wrong before the cost of repairing it exceeds its value as well.
All that being said, here are my general guidlines for you:
1. If you have a large screen, say wider than 8-to-9-feet, an older Runco might be a very good option. So would a Sony Qualia 004.
2. Don't expect the telephone-number contrast ratios that JVC touts to be matched by any older projector. That said, contrast ratios are only one part of the overall image quality equation and as long as you have a dark room, an older projector with a more modest contrast spec usually will be perfectly satisfying.
3. Provided you aren't going for that 9-ft large screen, don't forget to take a look at a new projector in your price point: The new Epson Pro Cinema 6020 (around $4000) looked pretty good to me at CEDIA and their advance replacement guarantee, no dead pixel policy, and included ceiling mount and spare lamp is additional incentive. The new $4995 JVC would also be a great option. Just don't expect to light up a big screen. (No doubt we'll now here from members here protesting that they love their JVC on their 12-foot screen; their mileage varies from mine.)
Edited by PF - 10/17/12 at 10:36am