I'm planning on using these guys:
http://www.baileymorris.co.uk/
I don't think they're the cheapest around, but they're not far from me.
The guys that run our engine test cells at work use them and recommended them to me.
Last year they quoted me £70+VAT to shorten one, and between £170 and £220 to make a new (MX5) one from scratch.
EDIT: You beat me to it mat2223!