A couple years ago, I decided to make a "temporary" smoking room. I have a covered back porch, so I framed a small 6' x 6' room off one of the patio doors using 2x3s. Covered the outside with R-4 as a wind break. I framed a hole up high on one side and installed a fan, leaving a small space up high on the opposite wall for cross ventilation. Cost less then a hundred bucks to do.
I have an 88k btu high hat, that I cut down, and built a custom base for, so that the heat is at head level while sitting. Added a 32" flat screen.
I was going to disassemble it during the summer, but saw a 5k btu window A/C unit at Sams for under $100. Framed a hole in the wall down low next to where I sit for the A/C unit.
Toasty in the winter, and nice and cool during those 90+ 100% humidity summer days.
I'm planning on building another at the NC house once I get it ready to move in. This one will be more permanent with 2x4 framing, R-13 insulation, sheet rocked interior, T-111 exterior, wiring and lighting. Should be able to do it for well under 2 bills.