For me this was an extremely low cost project as I already had a number of antique table leaves which I had found in my attic upon purchasing my home. since I didn't have the table that they belong to and they were a little bit on the rough side I decided to use one of those for this project as I have in the past for others.
All other materials I already had on hand from past projects as well so I really have no expenses to itemize. Depending on what you have on had and the type of wood you want to use this stool could easily be made for under $20. If you have to buy everything it could certainly be more.
1 3/4" oak board
latex wood filler
table saw (a circular saw could also be used)
router with round over bit
compound miter saw (table saw or circular saw could also be used)
block hand sander
rags & brushes
belt sander (or any other type)