How do specific tubeless valves compare to bodging it with a cut-off tube valve? How do specific tubeless valves compare to bodging it with a cut-off tube valve? Would the bodge work? Thanks
I've seen it done that way when the whole tube is split and used as a liner to make a tubeless system out of a non-tubeless wheelset.  As pointed out in the comments, if you already have a tubeless wheelset, the couple of bucks you save probably isn't worth the hassle you will experience trying to get the "bodged" valve to seal to the rim.  It might make more sense as an emergency measure if you have destroyed a tubeless valve.