Associate Price, Size etc with Characteristic

Hi, I would like to associate a price, size and weight with a given characteristic. I sell photographs and I want to be able to have categories for Print Type (mounted, unmounted) and size (12x18, 18x24, etc). Then I would like to set a price, size and weight for each variant. For example:

Mounted 12x18, $10
Mounted 18x24, $20
Unmounted, 12x18 $8
Unmounted 18x24, $16

The way I am doing this now requires me to assign a group of characteristics to a specific product (in this case a specific photographic image), then go through each variant and assign a price, size and weight. This means I am essentially enterng the same information over and over again. It also means if I ever change the price for a specific variant, I have to go to each print product and update them.

I imagine I must be doing this wrong, and there must be an easier way.

Thank you