purchasing power

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The ability to purchase, generally measured by income.
• noun The value of a particular monetary unit in terms of the goods or services that can be purchased with it.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun economics The amount of goods and services that can be bought with a unit of currency or by consumers.
• noun business The ability of a large collective or company to negotiate more favourable prices and terms than a smaller group or company.