Is $750 to replace the AC fan motor a fair price?

I have an AC unit at an old apartment of mine that's been off while I haven't had any tenants in it. I turned the AC on but it wasn't cooling. I went on the roof to look at the AC unit and the fan wasn't running so I pushed one of the blades with a screw driver and it started running, but doesn't sound the best. It's restarting when I turn the AC off and on again. I had two HVAC companies out to look at it and quote me on a fan replacement and they both recommend full unit/condenser replacement because it's 20yrs old. I'm looking to get this fixed as it will be a rental in about a month and I won't be around to fix anything, so I'm leaning towards replacement to not deal with issues. I'm also considering DIY options for the fan motor replacement but don't have a lot of time.