James,
I have a spreadsheet that might be of help to you.
Have a look here:
http://www.haynes.co.uk/forums/showp...23&postcount=9
In this thread:
http://www.haynes.co.uk/forums/showt...6923#post56923
Let me know if you want a copy.
EDIT: I can't remember if the costs on the snippet are those I paid. Seems mighty expensive. However, I do remember the steel costing alot more than I anticipated. Steel isn't cheap and it has more than doubled in price over the last few years.