different price lists for same image

I have imstore set up on my customer’s website (www.parofoice.com/wordpress – under the “gallery” tab).

We would like to offer each of the images as prints on either canvas or photo paper. The size options can remain the same, but we need to be able to set different prices for each size based on the type of print the customer would like to order (canvas or paper).

Is there a way to set this up easily? ideally where upon selecting “add to cart” the customer is presented with an option for the type of print in addition to size / color.

Any help is much appreciated.