I don't really understand.
I've attached a workbook showing what I *think* you want.
The conditional formatting in place for cells AAA!B2:B3 is like this:
=$B2<>VLOOKUP($A2,LOOKUP_TABLE,2,0)
If the price on sheet A changes, then the mismatch is highlighted in yellow on the AAA sheet.
This is the best I can offer given the information in the thread.
Hope that helps...