It took manufacturers four years to respond to the 1979-1980 Shah of Iran gas crisis. 1984 was one of the very best years for mileage. Cars were lighter weight and smaller engined than todays cars. Newer cars are safer and come at a cost of additional weight. Cars from the eighties are definitely not obsolete. Unfortunately they are all worn out and some parts are not readily available.
Cars were computerized (OBD1) between about '84 to '95. That was one more thing to go wrong. But it did provide flash codes to give a clue as to what went wrong.
1996 was the first year of 2nd generation On Board Diagnostics (OBD2). Nowadays a laptop interface is cheap and we can read our own error codes. That will sometimes really help diagnostics. A friends car had a miss. The computer said #3 cylinder was misfiring. That eliminated checking the plugs and wires and two coils for all four cylinders.
I like Ryder's strategy of taking the Ugly Discount; also the Readily Available Parts convenience.
My dad's strategy was to go for Low Odometer at low cost. Nothing else mattered. The lowest odometer at the least cost. He wound up with a herd of Simcas with low mileage. Invariably the starter motors had failed at 40,000 miles and the previous owners couldn't find, or didn't want to pay for, a new one. My dad would order them through Chrysler..... and wait.
In 1999 I systemetized my dad's strategy with this formula: Used-Car-Price/(100kmiles-odometer) = cost per trouble-free mile. I bought a 60k miles 1984 Chevy Cavalier, wagon, 5 speed, 2.0 liters, with a bad clutch for $600 and paid someone $300 to put a new clutch in it. So (600+300)/(100k-60k)=$ .0225/trouble-free-mile. At the time, the lowest trouble-free cost per mile was running at about $.05 or $.06. That Cavalier had the infamous pealing GM paint (Ugly Discount) and the Major Problem Discount.
In the formula:
Used-Car-Price/(100kmiles-odometer) = cost per trouble-free mile,
the 100kmiles is arbitrary. The assumption is that any car will go 100k without problems. A lot of cars will go a lot further. One could be more realistic and maybe use 150k-odometer. But I wanted a bias towards low miles on the odometer.
For freeway driving I'd recommend a Saturn with a manual transmission. They are light for their size. They are pretty comfortable and quiet. The older ones have a 1957cc (2 liter) engine and their tall gear ratio gives good mileage. All cars have their own characteristic problems, and Saturn's problem is cracked-head. Before buying a Saturn, find out when they figured out how to make heads. 1996 still had the head problem. A Saturn with oil in the coolant is not worth fixing.
For driving around town, and not needing to haul many people or much cargo I would recommend the 3 cylinder 1.0 liter Geo Metro.