Teddimac. Thanks very much. This is quite reassuring. I decided to quote him £400 for 11,500-word article. Which from what you say is alowish, reasonable price. I had been nervous that I'd overcharged.
I am familiar with the subject matter,so that shouldn't be a prob. I'm actually looking forward to it. It should be really enjoyable.
If a fairy gave me one wish, I might wish to be a translator -- of great novels. The combination of creativity and constraint involved in expressing the thoughts of one language in another must be a wonderful thing.
Also check out the ITI. Agree with Teddimac about not under-charging - the workload for you is the same whoever you're working for. The Translators' Association current minimum recommended observed rate for literary translation, which I base my rates on, is £88.50 per 1000.