Mine is old, I think 7 years? And except for the fact that I built up static electricity one day, zapped it when I adjusted the speed, and shorted out part of the display screen (and haven't gotten around to replacing it yet) it still works great. It was several thousand dollars new. I got it used for $450 from a couple of guys who trained for marathons, so they used it. They moved into a new house and didn't have room for it. It's taken me through two half-marathons and plenty of off-season runs when I really really want to run and it's a bajillion degrees outside since I've had it, and my mom also runs and walks on it.
Buying used you just want to make sure it's been used and not just sat around for a long time, because dust can build up in the motor when it goes unused for long amounts of time and can damage the moving parts.
That said, if you're being literal, 1980 is really frickin' old. I'm not sure how those would do. I mean, I know they don't make stuff like they used to, but wow. =P
I wouldn't expect a Wal-Mart treadmill to last a REALLY long time. The biggest difference between a treadmill and any other kind of fitness equipment is the motor. The money you pay is really for the motor more than anything else involved on the machine. So it depends on how long you expect it to last. Mine was an investment, I don't see a point in time where I expect to NOT be a runner anymore, so I wanted one to last and last.
As a compromise, if you have a Dick's Sporting Goods nearby, you might try there. They have some Livestrong treadmills that are about middle of the road, not cheap Wal-Mart ones but also not the very expensive gym quality ones you might find elsewhere. And you can often find them on sale and get a pretty good price on them. I think they are nice compromises and they seem to last a fair amount of time. They are not quite in the $200-300 range, closer to $500-600, but a treadmill is something worth investing in if you expect to use it for a long time.