penny-wise and pound-foolish
Prov. thrifty with small sums and foolish with large sums. (Describes someone who will go to a lot of trouble to save a little money, but overlooks large expenses to save a little money. Even in the United States, the reference is to British pounds sterling.) Sam: If we drive to six different grocery stores, we'll get the best bargains on everything we buy. Alan: But with gasoline so expensive, that's penny-wise and pound-foolish.