Is your garage walls and/or ceiling insulated? If not, most any refrigerant type cooling unit will be working extra hard just to keep up. If the garage is insulated, you should be happy with a mini split or window unit. However, even though you have no windows in your garage, it is not a big deal to cut and frame out a hole for a window A/C unit to fit into. The advantage here, is you can put it up high where it will take in the most heat. The mini split units like to be mounted up high as well. Of course being high is not as good for winter when you need heat, but the cooling aspect of these systems is where they really do well.

If your shop has insulation you should be ok. Our shop at work is metal construction 25x50' with 14' ceilings and currently cooled with a 2 1/2 ton Rheem unit from '96 that's on its last legs. When new it could keep it 75 on the hottest days, now it struggles to keep it at 78-80 when it's 100+ outside. When it gets replaced this fall we're considering upgrading to a 5-ton and adding a currently un-conditioned 25 x 25 production room to the system.

That was exactly my thought. For $1000 savings, I'm cutting a hole in the wall.

There are window unit heat pumps too, which will heat as well. Make sure they're actually a heat pump, many are just a normal AC with a built in electric resistance heater. Fine if that's what you want, but way more spendy to run than a heat pump.

If you have no insulation and you're selling the house anyway, skip installing an A/C, it won't really help anyway. Open the door and park a drum fan out there to move some air.

I just installed an 18k btu minisplit unit. I had done a 12k in my kitchen a few years back. Amongst the best decisions Ive ever made regarding climate control,in a building. Super efficient, quiet, and the ability to throttle the compressor means you can always get the right mix of cooling and dehumidification.

A decent unit, all in, is $1200-2000 depending upon size and capacity. Avoid fly by night units. If you can work on old cars, you can do the flaring and vacuum to get the system ready. Really not a lot to it...

With no insulation in the garage, any heating/cooling system effectiveness is going to be seriously compromised.

Depending on your timeline and the value added to the property by having an insulated and climate controlled garage, I'd consider doing it anyway. You could very well wind up making money on the improvement.

I just insulated my 30x30 two story tin-wall shop. R7.7 foam panels on the walls and R21 fiberglass on the ceiling, as well as a goodly amount of caulking and expanding foam. ENORMOUS difference. Absolutely enormous. Looking forward to seeing how it does this coming winter - last year I was thrilled when I was able to get the snow I'd tracked in to melt.

True, but this isn’t a situation where the unit will run 16-24hours per day, every day. Not to speak for OP, but garage service is more like a few hours, a few days a week, if that. Often ultimate comfort isn’t a necessity compared to taking the edge off.

Isolation is the key.
 

I like not having windows. No one can see what is inside and windows are a source for heat transfer.

R40 in the attic, a good window unit mounted high and a low electric bill for cooling. Blown in insulation is the best especially if batts were used first.

The sweetness of doing it cheap will be long gone when the bitterness of high cooling/heating cost are realized then endured.

Lol

Material is less than $1k.

Rule#1: if any company sends a salesman to your house for a quote I guarantee they are overcharging you.

The insulation is kind of a big deal if you want to do anything more than take the humidity out of the air. Insulation is cheap and effective, which is why it’s not recommended by your ac installer. Just buy a bigger (more expensive) unit!

With this statement alone I'd have told him to get lost. He's either completely ignorant of HVAC, or he's a liar trying to sell you a bigger system. Either way, gone.

Obviously get multiple quotes, research insulation, and look at DIY mini split or hacking a hole in a wall to install a window unit.

A window unit is totally a viable option. Basically cut a hole in the wall and you can have heat and air in a half a day.

Mini splits can be bought on eBay. I bought mine 2 or 3 years ago and has been working flawlessly since. It was $550. It took me a full day to install, it was my first time installing a split system.

I had a real struggle trying to get my flares right, I didn’t have the correct flaring tool. I ended up brazing the line. Looking back I should have left the line in tact and just installed it. I wanted it to be super tidy so I went through the extra effort.

Don’t over think it. If you plan on being there another year or so I would definitely do it. Insulation and drywall will make your garage more like living space than, well, a garage.

I’d show you a picture of my garage but this forum is from the 90’s and can’t handle anything bigger than a thumbnail.

Garage