I haven't done the research into the drivetrain in either car, but on the face of it I'd think your greater risk of pricy repairs are in the Avalon. If the engine in your Kia does die, I have to imagine replacing it would still be cheaper than replacing the engine in the Avalon for the added complexity of the hybrid system.
You do you though. If your heart says you gotta have that 250k mile former taxi Avalon, enjoy it.
Honestly, I'm shocked it could get going that fast.
Assuming you are asking for installation advice, please consider hiring a professional. I am no stranger to diy projects and thought I could adjust and fix mine on my own and ended up snapping the spring. I tried to figure out what to replace it with but ended up calling out a professional. The door now works far better than it ever did and I know I could not have done as good a job.
What would you recommend I eat there? I have been to Culver's several times and have yet to be impressed. Please, show me the way.