I've tried cloth electrical tape, but I think it often is sticky on both sides and makes a bit of a mess.
Do you have single walled or double walled rims? The tape requirements may be different for the two, as the single walled rims just needs one to cover the nipples, and the double walled rims need support over the holes.
Cloth handlebar tape may also substitute for rim tape, but probably isn't any cheaper than the rim tape.
With newer tighter fitting tires/rims, I've pretty much given up on the cloth tapes, and started getting plastic rim tapes. Usually ordering a few from overseas bike shops.
I have intended to experiment with various heavy duty tapes, like packing tape, but ultimately it wasn't needed.