Once used wine corks from boutique and small premium wineries, almost exclusively Napa, Sonoma, Mendocino, Amador and Monterey counties.
Selling gallon bags filled with 100 used wine corks for $10 each. These are great for craft projects, displays, cork backsplashes, cork bulletin boards, cork trivets or coasters. Online, these corks retail for $20 plus shipping for a set of just 50! Cost here is ~1/4 retail.
See: http://www.wineenthusiast.com