A person who is economical or thrifty; someone who carefully saves and avoids wasteful spending.
彼は節約家で、外食はほとんどせず自炊をしている。
He is thrifty and hardly eats out, cooking for himself instead.
節約家の祖母は電気をこまめに消す習慣がある。
My thrifty grandmother has the habit of frequently turning off the lights.
節約家というより倹約家と言った方が近いかもしれない。
It might be more accurate to call them a frugal person rather than simply thrifty.