"I don't offer a lot of my art on digital because its signed and it's art, not photogaphy. "
I am not sure I totally understand this statement, but for the most part, I don't think the overall general, art buying public is all that interested in what is art and what is photography (your separation, not mine) and what is digital and what is is not.
I think for the most part, if they like the image and like the price, they buy it. And I would price them all the same on all of the different products.
And your Iguana Wish You A Merry Christmas is fantastic! I love it on that T-Shirt!