An inexpensive fan is a used furnace fan (sometimes you can get them for free). The average furnace fan will create 1000-1500 cfm on high speed.
Build a plywood box for it to create a framed rectangular outlet. Put it on a wooden frame with casters of proper height to roll it in place then store it out of place later. Use it to suckout the air (not blow fresh air in) , sucking creates less turbulence for stirring up dust. I made a removable plywood adapter so that I blow out of a window.
On other end I open a window that has a screen on outside and then tape cheap throwaway filters on the inside of the window.
You will get some paint buildup on the fan, but for occasional use that won't matter. Always let your fan continue to run for several hours to exhaust fumes b4 unplugging.
The cheapest, best air filter for water removal is is motorgaurd toilet paper air filter. Place it before you regulator with some 3/8" or 1/2" ball valves so it can be bypassed when not painting
You do not have to use their filter element, just buy a pack of cheap toilet paper (the ones where the rolls are slightly smaller diameter than the deluxe units). You will be able to paint the whole car with one roll. ALLWAYS take the filter element out for non painting jobs because the wet paper will eventually corrode the aluminum housing (ask me how I know). You can let the roll dry for a week and reuse it over and over.
I have painted ~ 15 cars using this method.