Economize

Economize \ih-KON-uh-mahyz\ , verb;
1. To practice economy; avoid waste or extravagance
2. To manage economically; use sparingly or frugally

This word dates to the 1640's as "to govern a household" from economy + -ize. Economy, meaning "household management," dates to the 1530's from Latin oeconomia, which was borrowed from Greek oikonomia ("household management, thrift"). Oikonomia evolved from oikonomos ("manager, steward"), which is a compound of oikos + nomos ("house" + "managing"). Economy as in political economy ("wealth and resources of a country") dates to the 1650's.

Using economy as an adjective meaning "cheaper" didn't come about until the early 1800's and was originally an advertising term. By the 1950's the meaning had evolved into "bigger and thus cheaper per unit or amount." The first Costco didn't open until 1983.