I'm in Alabama and working out of my garage with my "temporary" ventilation for almost 2 years. I don't have air conditioning in there either. Oh, and it's only 95 right now, but we get humidity to help make up for the difference in Arizona heat!
I needed to be able to put up and take down my ventilation quickly and easily. I didn't want to spend a lot either.
This is what I came up with:
http://community.webshots.com/user/seabeads
If you don't want to lose too much air conditioning, I would "pipe in" air from an outside source to come in right under your vent fan. In that way you will draw out the unconditioned outside air and be able to keep more of your cool air. You can use the same window for both if you had too, but you would need to run your intake ducting to at least 10 feet away from your exhaust area.
Caveat - I am not a role model for ventilation, but this is working well for me and I think I am pretty safe. I use a disposable 3M 8233 N100 Respirator rated for metal fumes for my rare "heavy metal days". I am also only using a Minor Burner with soft glass. A bigger torch has bigger needs.
Joanne