Dynamic price feed

Hey all.
couldn’t seem to find any threads about it, otherwise, could someone redirect me please?
But does any one know if it’s possible to make a widget, or maybe code a dynamic price feed for products?
Let’s say i’m displaying a tea cup in two different sizes and the smaller one is cheaper that the larger one. Letting people choose in a drop-down menu between the two, is it then possible to to have a dynamic prize that changes dependant one what size people put in the basket?

It baffles me if i’m the only one thinking about this? Has this been done on Readymag before?

Kind regards
-Ben