Cheap is a pretty relative term. But if you mean really cheap:
You can fold a piece of paper with your Grandfather's name on it and use that as a menuki.
You can go to Target or some similar store and look for a cheap pair of costume jewelry ear rings with dragonflies, or such.
You can carve a piece of bamboo or scarp of ivory.
Go to flea market and look for some neat small item.
Rummage through the garage drawers.
Use an old coin ( Indian head penny, Barber dime, British Shilling, Japanese coin with a hole, etc.)
Etc.............