Rawk, Chateau Romani is canonically worth 200 rupees in its land of origin, and Romani Ranch isn't exactly far from the Milk Bar so it's not like they'd charge extra for transport fees or whatever in Termina. It makes no sense for Link to go "oh he could've paid for five with what he paid for this one" when 300 rupees is probably cheap for getting the stuff outside of its land of origin.