I found it useful to cut a small square of Magic Eraser into a wedge shape and glue it to a silver coin. A gold coin would solve the low-cost problem.
If you decide to glue the Magic Eraser to something, make VERY sure that the something, like a coin, is not magnetic. The cartridge magnets are strong and can attract anything magnetic, and that can do damage.
If you decide to glue the Magic Eraser to something, make VERY sure that the something, like a coin, is not magnetic. The cartridge magnets are strong and can attract anything magnetic, and that can do damage.