Attributing Values and multiplication

I am writing a spreadsheet as a report for a customer and i want to show the following in the sheet.

A customer buys 12 of XProduct (retails £2)
A customer buys 15 of YProduct (retails £3)
A customer buys 20 of ZProduct (retails £5)

I want the sheet to have columns stating - Amount Bought - Product - Gross Amount.

And i want to be able to have the product column intelligent enough to know that if i type any of my products sold it will automatically attribute the correct cost (i.e. I type in Xproduct and it knows that value is £2) so that in the Gross Amount column it will all make sense, and save me having to manually put in the retail cost each time which will occasionally change. At present i have the same three columns and i multiply the Amount Bought with what i know is the cost and do the sum myself and then enter the result in excel - so i want to save time. Can this be done?

I am new to excel, hope you can help

Thanks for pointing me in the right direction, but that only made my scratch my head even more. I suppose I am really trying to say that i only know how to do the most basic of formulae and not sure where to start with Vlookup if indeed it is the most obvious, simple, and best method.

Ok, i have attached the zip file for your consideration. As you will see, the elements i ideally would like costs attached too are in the Content Sold area - Wallpaper, Games, Ringtone etc. with costs for each.

Many thanks

Thank you very much for your help. All i need to know now is how that formula does what it does, so that if i do something similar i can replicate it. Thanks anyway.