So a few weeks back we painted and added 2 shelves on each side of the main windows in the dining room.
Two 1/2" x 7" x 8' Primed MDF board
Twelve - 1-in x 8-ft x 6-in Paint Grade Interior Pine Corbel Bracket Accent Lowes link for bracket
Two 1/2" x 2" x 8' Primed MDF board
E-Z Ancor 20-Pack Stud Solver Drywall Anchors Ancor link from lowes
I think the cost came in around $70. Or about $17.50 for each shelf.
We could have saved some money by not using 3 pine brackets and using 2 metal brackets or even just making our own brackets. However I don't own a router and the Mrs wanted something halfway decent.