Microsoft Excel (2010) expert required to create complex formula

Project Description:
We have a simple Excel workbook that contains a list of students and scores. The scores are represented as an alpha character. One of the worksheets contains a look up table relating the alpha character to a numeric character.

For each of the columns (subjects) I need the average score calculated in the last cell with the letter converted to a number value. I.e. convert the alpha scores for each subject per student to numeric value, then render the average taken using the number of subjects as the averaging value.

Please only bid on this if you have previous detailed knowledge of Excel formula and VBA functions.

Project is urgent and will be awarded very quickly for immediate completion.