Buy the '89, I guess. You sure you couldn't buy a 4 or 6banger, 5spd, maybe something '91 or better with maybe half the miles on the OD those have? Hopefully you are at least getting the '89 dirt cheap - like less than $1500.
My YJ4 only has around 140k, and, between 65k -140k, I've basically replaced everything that can wear out. Maybe the last owner did the same on this '89. Or, maybe not.
If not, you may have a lot of expensive stuff that you'll have to replace before too long (even if you never go offroad) such as the following: shocks, stabilizer, bushings, engine mounts, brake rotors/lines, brake pads, tires, front seats, radio, speakers, top, ignition system, battery, all fluids (synthetic), alternator, starter, power steering, water pump. You may want an alarm, security gear (tuffy center console and trunk). Typical performance upgrades cost money and we are not even getting in to off road stuff like lockers, lifts, larger tires/wheels, regear etc which will really run up a tab.
So, get the '89 (But, you may find that you will save money in the long-run if you get a later, '91 or better, fuel injected 2.5 or 4.0, 5spd with half the miles on the OD versus the '89)
Good luck. :)