Add custom field per product variation

Hi there!

I have a product (a photo book) with several variations (different sizes and amounts of pages). Is it possible to add a different custom field per product variation? In this case it would be a counter to add extra pages to the book with an price per extra page added (I know this is a premium feature, will buy it soon). The tricky part is the cost for one extra page is different depending on the size of the book. Hence, is it possible to have a different custom field added to each product variation and if yes, how?

Many thanks,
Chris