I want products to show no price until options are selected

Hi again
My products, which are prints have no price until the size options are selected. For that reason I don’t want to show a price with the listing of the product until a size is chosen. How would I set that up? At the moment I have it set up as the base price for a 8×10 print and then each increase in size has an added price. But it really doesn’t make sense that way.
Thanks for your help.
Ellie
https://www.elliekennard.ca

https://www.ads-software.com/plugins/orillacart/