I was driving home one day and saw a sign '18,000 BTU AC for sale'
They just had central air installed and didn't need the old Kenmore anymore.
I took it home as a spare for my 30 year old 20,000 BTU Chrysler AirTemp.
Sure nuff, about a year later my wife turned on the AirTemp on a warm spring day,
forgetting to remove the winter cover, and almost set the thing on fire. It was smoking!
I had to open up the hole-in-the-wall for the larger Kenmore, but it works great.
Using less power too. Got 3 years out of it so far.
I slide the guts out of the case a bit and oil the motor every spring, when I take off the cover.
Many times people sell them when they move out of their home.
Check your local Craigs list and news papers.