LEGO Classic 10″x10″ Building Baseplate (Green or Blue) $5 each at Amazon
Amazon has the LEGO Classic 10″x10″ Building Baseplate (Green or Blue) for $4.99 each. Shipping is free with Prime or on orders over $25.
Walmart.com has the LEGO Classic 10″x10″ Building Baseplate (Green or Blue) for $4.99 each. Shipping is free on orders over $35.