Oh, right, you're in the same situation I'm in: no shops anywhere within reasonable travel distance? Almost certainly, shipping cost is charged by weight, but in steps, so ordering a couple of bottles of paint will cost the same for shipping as when you order just one. What I would do is ask myself what else I need from wherever you order your paint — more paint colours that you don't have yet, new knife blades, a set of crew figures etc.? Not that I would recommend buying things you don't actually need, though. Rather, it's smarter to figure out what you do need so you can buy it all in one go and save on postage.