VBA script to compare New and Old Budgets

I am trying to automate via VBA, a model to compare two budgets, a new cost budget and an cost old budget, determining the variances between
(a) Q-columns(Volume of products)
(b) I-Columns (Value of cost budgets for products)

I need to use the Look Up Keys(built by concatenating columns K,L,M) to find the corresponding variance between columns Q of NEW and OLD Buds and produce the output on the 'CHANGE' sheet(Column Q). The same is applied to the values in Columns I on NEW and OLD Bud with the CHANGE sheet showing the variance in Colunm I.

I have a large number of cost-budgets to compare for a large portfolio of products. I have attached example files (excel 2003, 2007). Thank you for your help in advance.