Traverse data from one excel tab to another in same file.

Hi guys, I need some help while doing some analysis which will save me a LOT of manual work. I am hopeful someone here can help me out, as they have done before and it has always worked.

I have created a sample file (attached) to help explain what I want to achieve.

I have two sheets in the attached file. GM and ROAM_COST

The formula is needed in GM sheet. For e.g. I want the formula in cell B2 in 'GM' to look at the combination of A2 and B1 (also in GM) and check this combination in sheet 'ROAM_COST' and give me back the value. In this example the value will be '2,44'. This formula should then work for all cells when I stretch it across and down, every time, checking for a new combination in column 'A' and row 1.

Hope this is clear enough, but if not, please do ask.

Ali