Advice on keeping an old car with 280k+ mileage maintaned/running?

Make sure to keep up with your routine maintainence; tire rotations, oil changes, air filter, ect..... If you don't see any leaks visually on the motor or under the car, then it's most likely pushing oil through and burning it off. If you have the money, some top end motor maintainnence should give you quite a few more miles!!!!! Good luck.

Get rid of it or it will drain your wallet.

If your engine goes through more than a quart of oil every 1500 miles then start looking at a rebuild, however since you didn't pay for car, just run it till it dies. Follow Trelby's advice on maint. to keep your vehicle in top shape. Toyotas will surprise you how long they will last. I've seen them run to 600,000 miles before a rebuild!!!

Do a compression test. After the car sits at least over night will the exhaust be dark when you first start it? If so then the oil loss is from leaky valve seals. High milage motors often burn oil due to the piston rings being worn as well as the cylinder walls. It's not worth rebuilding unfortunately. When it dies find a lower milage used engine for it and put it in yourself. The car is not worth it to have a shop do the work. All used cars will need repairs. When a repair costs as much as a decent used car it is time to recycle the usable parts. Unless the value of the car is substantial of course.