Garage too hot; Portacool versus mini-split A/C system?
 

Those evaporative coolers aren't real effective when the humidity is high. You didn't give a location, but the use of "heat index" says you are probably in a high humidity situation. AC is MUCH more effective in that situation.

If it's crazy hot, I just put a shop fan blowing directly on me and dampen my clothes with water, not dripping wet, but enough to know it's there. Only 100% cotton t shirts and jeans or work khakis. Same principle as the swamp cooler, but far more effective, as it is directly on your skin. Have to wet down every 30 mins or so.

Where are you located and what is the ambient humidity level? Look at the weather and see what the dew point is, that is the absolute minimum temperature that a swamp cooler can provide. High humidity (>40%) will make it useless or make the indoor temp WORSE (high humidity). You also need free flowing ventilation, preferably a cross draft for the swamp cooler to do its magic.

FWIW, in my area the humidity in the summer time is ~20-30%. On a 100˚+ day, the swamp coolers we have in our warehouse will blow in the mid 60s, keeps the overall temp in the warehouse in the upper 70s, lower 80s depending on the time of day and the humidity level. The key for successful operation is LOW HUMIDITY.

I'm in the same boat in Columbia, S.C. ...

Mini Split is the ticket. Less than a grand and it looks like something a DIYer could do. I've been talking about this for years and just maybe this month ...

Evaporative coolers will not do much for you this time of the year with the high humidity there. I used to do business in Charleston, went thru the same. A good ac is the way to go.

I agree .... mini-split is the ticket. HD sells them for around $900 and refrigerant will be around another $90 and the odds and ends needed probably another $100 So, for around $1,100 you can be chilled ...

Yup, humidity is too high for much effect, and as said above, added humidity in the shop will make it feel hotter unless you are standing in front of the cooler.

Is there a window in the garage? If so, a window unit from BLowe's or Home-Repo is a nice cheap solution. A 12K BTU should cool the garage down in a hurry and still be able to cope with the heat rejected from the cars.

A window unit will work just as well as a mini-split for the same BTU. A 12K BTU window unit is $200-250, a mini-split is more like $1200. Installation for the window unit is under 30 minutes, mini-split is several hours. If there's a window to slot a unit into, it's a no-brainer.

In order for a Portacool to work in high humidity, you will need additional wind speed to give effective evaporation. We're talking nearly a wind tunnel experience.

Back in lean times, I installed multiple whole-house fans to provide sufficient cooling. It won't lower the temperature that much but is more tolerable. You will need to lower the garage door to about 4-6".

I bought a mini split off eBay about 3 years ago for $550 delivered. My garage is 2.5 car detached with 10 ft ceiling- insulated and drywall. 12k btu unit keeps me toasty warm in winter and is more than capable at cooling.

It’s also nearly silent which is a big deal to me.

I have been having the same thought, sort of, except I am contemplating how to cool my 40x60 shop with 16' ceilings. It is insulated but thought about getting a 5 ton unit, run a line of ducting down the center with vents. It might not make it cold but surely it would cool it to a tolerable level for the few hours on the weekends I am out there.