php program to calculate find the cheapest product price

This project requires a 2 small functions. The 1st function: that will calculate the cheapest price for a given grocery item ( with or without the barcode) found in various locations. The item can be based on the unit value or unit weight, for example if item A is being sold @ 3 units for $5 in store ALPHA, and the same item A is being sold @ 1 unit for $1.50 in store MEGA. which is cheaper? The php function or program should be able to determine the cheapest item. The second program is a trip cost calculator. It should function as the following site: [login to view URL]