I want to say it is somewhere between $15-$20. Here is something interesting I read on another site....
Mr. Potato Head Hints
A popular souvenir is the all-you-can-fit-in-a-box Disney-themed Mr. Potato Head toy. This is available at Engine Ears Toys, just inside the entrance of Disney's California Adventure, and possibly at other locations within the resort. For a flat fee you get as many parts as you can manage to fit into the provided box, as long as it closes and is not bulging. Here are some hints for getting the most for your money when buying this toy:
* If possible, buy one or more basic Mr. Potato Heads while you're still at home. You can get one cheaply from a discount store (or even a thrift store or yard sale, if you're really frugal). The head sold at
Disneyland is the same as the standard ones sold elsewhere, and it's the bulkiest part. Since will take up a lot of room in the box, skip it and load up on the Disney-exclusive parts! You may be able to make up multiple complete sets if you buy the heads separately.
* If you do buy the head at Disneyland, be sure to open up the back and fill it up with parts! This is allowed.
*Be sure to get plenty of arms at Disneyland. The arms are different from the standard arms that you can get elsewhere, and they allow you to attach special Disney items like Mickey ice cream bars, video camera with Mickey ears, balloons and autograph books.