There was a recent thread on this forum on the Harrison changing tent. Here is an inexpensive solution that I came up that, though not intended to replace the Harrison changing tent, might work for people who don't need 100% light protection to change film in full daylight.
What I have found is that there are very few times when I want to actually change film in the field in daylight. My most common problem in working with ULF cameras is trying to find a place inside at night that offers enough protection from light to change film. Motel and hotel rooms almost always have extraneous coming in from somewhere that is often difficult or impossible to block.
My solution to this was to take one of the small dome kits intended for kids and treat it so as to make it light proof enough to use in the above conditions. The one I use is 6'X5' and sets up very easily almost anywhere. To dark proof it I first sprayed on a couple of cans of the rubberized paint that is used to coat tools, then finished it off with two cans of silver metal paint. The result is a small dome tent that a person can tclimb into with plenty of room for changing any size holder, up to 20X24" if you want to go there.
The finished tent offers what I consider 100% protection for changing film inside at night, with the main lights turned off, even with a fair amount of ambient light coming in through doors, windows, etc. I have recently sealed off the breathing vents at the top of the tent and it now appears to be light tight even in direct sun with everything zipped up, though I would only use it in these conditions in an absolute emergency.
Total cost less than $40, including $18 for the tent at Wal Mart, and $20 for four cans of spray paint, two rubberized black and two of metallic silver. For use in full daylight I think it would need a couple of coats more of the silver metalic paint.
BTW, I have seen even smaller versions of dome kits intended for very small children that might be even more practical for some uses.