Automatically input data from created database based on inputs.

[Gnomenclature]

I have a database consisting of 3 columns and endless rows. I would like to be able to input data into column a and column b and have column c automatically filled in.

For example I have been tracking the cost of groceries at multiple stores so that I can better forcast my expeditures. I shop at 4 different stores: ALDI, Food Depot, Wal*Mart, and Costco. While shopping I track the store I am at as well as the dollar amount of each item I buy.

I.E.
Cheez-Its - Food Depot - $3.52
Cheez-Its - Wal*Mart - $3.73

I have this database built and it is still ever expanding. On a seperate sheet I would like to be able to enter the item and store and have the appropriate output price automaticall filled in so that I can print a clean grocery list before my weekly shopping.