For everyone that says a mini split or AC, how big is your space and what's a rough estimate it costs per month during summer to run it? Do you turn it on in the morning and run it down to as cool as the house is, or leave it on 24/7 and maybe only set it at something like 80 degrees?
I’m going to try to answer your questions but my use of my mini split may not be typical.

My garage is two bays deep on one side and a single bay deep on the other.
The shop bay shown in the above picture is a bit more than 16 feet deep and 11.5 feet wide.
The two bay area where the vehicles are parked is 20 x20 feet.
Not ideal, but typical for an Arizona builder.
Garage has a 10.5 foot ceiling height throughout the space.
Again, typical of an AZ builder, there was no insulation in the garage walls or ceiling.
House was a spec. so I had no choice with the builders stupid decisions.
I cut an access hatch in the ceiling and had a contractor blow in a **** ton of cellulose insulation.
I insulated the garage door using rigid foam panels and a radiant barrier.
You can see the mini split on the LH wall directly across from my woodworking bench
I use the mini split more like the swamp cooler in my previous AZ house than the use your questions asked about.
The A/C is turned on when I work in the shop bay. It is turned on when I start and turned off when I’m done working. I usually leave it run when I break for lunch.
Note: The garage metal surfaces heat soak to just over 100* during times A/C isn’t used.
Welcome to Phoenix!
Temp set is at 80*, blower speed from 75 to 100% during use
The fact that the unit blows right into the main area where I’m working makes it very comfortable compared to working in the area during an AZ summer of 110*
The fan on the back wall is key. I aim it at the area where I’m working.
For example, I’ll pivot it to the left if I have a lot to do at the drill press or table saw.
The cross wind makes a noticeable difference.
Given the size of the garage and the lack of wall insulation the mini split helps but certainly doesn’t cool the area where vehicles are parked to the same temp as the shop bay.
If I’m under the hood I may add a box fan on the metal bench or table saw table.
Again, maybe unique for the way I work. Not perfect but better than no A/C.
I do miss having the garage door open but……
I really can’t answer about the increased cost. It’s not much.
The average daytime temps outside make more difference in my monthly bill than the A/C costs.
Maybe not the ideal set up, but it allows me to work well into the afternoon during the hottest months of the year.
I built 6 pull out shelves last July. No way would I have started that project at that time of year before installing the mini split.
Hope this helps.