Help Comparing cost on two work sheets to update cost

I am trying to figure out how to update cost from a vendors .xls file I want to compare my price list to the vendor price list by OEM number and Highlight any cost that have changed and show the amount of change. I have really tried and tried but I cannot figure out how to do the formula correctly. Any help would be greatly appreciated as I have to do this manually now and we have 4000 parts from this particular vendor.
Thank You
Matthew