Please see Store Price Change.
The OP doesn't need to do the initial step of the Quick Install instructions as they already have jQuery installed.
This actually turns out to be harder than one might think. It's not just a matter of throwing some CSS at it. The way the structures are built and SS is manipulating those structures under the hood when variants are involved and one is changing menu selections makes this tricky. Basically the price text is being rebuilt on the fly when the user interacts with variants.
Let us know how it goes.