If you are shrewd in your spending, you can make a small salary go a long way. Use the adjective shrewd to describe a person or thing that is smart or clever in a practical sort of way.
The word shrewd is from a Middle English adjective formed from the noun schrewe, "an evil person, a villain." This Middle English noun is an earlier form of our modern English word shrew. So shrewd and shrew are related to each other. Shrewd doesn't usually have a disapproving or negative tone, but shrew certainly does.