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.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)