A person who lives simply and economically can be called frugal. Buying clothes at a consignment shop would be considered frugal. Not getting your mom a gift for her birthday — that's just cheap.
Thrifty, spartan, and prudent are synonyms for frugal, a word that often has positive connotations when used to describe a person who lives a simple life. "The question for retailers is whether shoppers will remain frugal or slowly resume their old spending habits whenever they get more money in their pockets," wrote The Wall Street Journal. You might also speak of "a frugal meal" — a very plain, cheap one. The word is from Latin frux, meaning "fruit" (in the sense of "profit").