By finding an old saw blade at a flea market or rummage sale, the cost of this project can be greatly reduced, but you will need to sand the blade down to the metal, and apply a primer (You can get this in the spray paint section of any hardware/department store).
Once the primer is dry you can paint anything you want on the blade.
Don't forget to spray a clear coat on after the paint dries.(This is found in the paint section also or in craft stores everywhere). Let dry and hang on the wall to enjoy!