Here are a couple of links to ideas. The first one is a decorated coffee mug. You can usually find these for a dollar each at dollar tree or dollar store.
Father's Day Crafts: Dad & Me Coffee Mug - Kids' Gift Ideas for Dad - Kaboose.com
This one would be cheaper to do.
Father's Day Crafts: Dad Rocks Paperweight - Kids' Gift Ideas for Dad - Kaboose.com
Hope this helps.
Dianne