I had one 10,000 BTU (0.83 Ton) window unit to cool a 1000 sqft room. Just about did the job. Then I put in a 4.5 Ton (54,000 BTU) central air unit to cool the whole house (2500 sq ft.). I also included an Energy Recovery Ventilator ($500 - $1000 on Amazon) which is basically a heat exchanger that pulls inside air and extracts the cold (or heat) and exhausts it outside, then pulls outside air through the heat exchanger and extracts the heat (or cool) and injects it back into the space. My summer electricity bill went down by 20%.
The ERV has a pretty powerful fan, but it also engages the fan in the main furnace air handler when it's on. I wonder if you could just use an ERV and just a cooling coil/compressor (maybe 1 or 2 Tons) to cool the garage with the side benefit of constant air re circulation summer and winter to keep the air fresh as a summer breeze.
I talked with my son who is a Mechanical Engineer and an Architect and he said those window units are terribly inefficient because of space constraints to fit in a window. I'd be happy to gift you my 3-year old LG window unit, but it weighs so much the freight would be twice what it's worth.
Here's a link to some ERVs on Amazon
https://www.amazon.com/s/ref=nb_sb_ss_i_1_26?url=search-alias%3Daps&field-keywords=energy+recovery+ventilator&sprefix=Energy+Recovery+ventilator%2Caps%2C502&crid=3VOWG06RYJ82Y),
And here's a 2.5 Ton A/C evaporator and coil for $1261 (free shipping)
https://www.amazon.com/Goodman-R-410a-Downflow-GSX130301-CAPF3030A6/dp/B00WSBXUK6/ref=sr_1_4?keywords=central+air+2+ton&qid=1564933170&s=gateway&sr=8-4I'd save up and make the investment rather than skimp after you've done such a fabulous job building the garage. Pitch the energy saving efficiency of the ERV to Lana. Save the Planet!