Here's my solution for venting the booth out a nearby window. I was at Lowe's Home Improvement and it just kind of came to me. 
I bought a $15.00 telescoping / adjustable length low-profile dryer hose duct that is designed to take the place of the flexible dryer hose between the back of the dryer and the wall of your laundry room. It is made of thin aluminum sheet metal, with a round hose flange on either end (opposite sides). You can adjust the length of the unit by sliding the 2 overlapping rectangular ducts over one another.The dryer hose coming off my spray booth clamps on one end (indoors), and the other end got an exterior dryer vent flap thingy attached to it (outdoors).
I simply closed the window on top of it and cut a piece of wood to block the window closed (for security). I also got a roll of self-adhesive foam weatherstripping to seal in all the gaps. It has worked wonderfully for the last 10 months; winter and summer!
The whole thing, hose, clamps and all cost me about $20.
The only downside is, that it also sucks all of the ice cold A/C air out of my model room.
