LightInTheBox offers the Parallel 12" LCD Writing Tablet in several colors (Blue pictured) for $13.99 with free shipping. (Choose "Postal Service - No Tracking" shipping during checkout.) That's the lowest price we could find by $6, although we saw it for a buck less two weeks ago. It features an erase button and comes with a stylus.
Note: This item ships from China and may take 11 to 18 business days to arrive. Uncheck "Add Shipping Insurance to your order" during checkout to remove the 49-cent fee.