Suppose two objects are on sale. A is cheaper than B. Is it right to say that B is more expensive than A (although both are cheap)? Does it depend on the context? Suppose I go shopping with a friend, I see something I like at an irresistible price. Could my friend say: "Donīt buy it here! Itīs more expensive here than at blablabla..."? Or would he say "Itīs cheaper at blablabla than here"?
You can use 'cheaper than' or 'more expensive than', whichever you prefer.