You could probably do a lot of insulating of the garage (even the door) yourself...it would be cheaper than hiring someone, & save money in the long run.

With your garage being so much smaller, you'd probably only need 1 or 2 up-ducts; I don't remember them being very expensive to install either- those who
work on HVAC should know all about them, & maybe you can find a good handyman to install them for you. They work simply & by themselves, a win.

But now that I think about it...my garage was "finished" meaning I also had a ceiling...you don't, right? So you'd just need venting above to the outside.
But same idea, cool air sinks, heat rises...they make fans for attics etc...you might want control for the seasons?