$30 is a fantastic price. I'm sure it would be higher today, but even still it might be worth it just to have it be someone else's problem. I use a cement along the inside of the seams to improve the strength and light-fastness, so I let them dry overnight before reassembling. I've got it down to about two hours of labor from unscrew to screw. Not sure about the materials, maybe $5 or so per bag, depending on what I have around.
I have yet to make a new bag for my mag. I took it apart, drew out a pattern, but have been busy with other projects on other cameras. I still have two bag mags in good condition for my 3x4, one each for my 2x3 and 4x5. I also have a 3x4 Speed with a Graflex back, so I can also use the bag mag with that one.