contracting/Freelancing

What sort of rates do you charge as a freelancer or a contractor? Or more precisely I want to know what sort of rates *I* should be charging. There is the possibility that the Beeb will want to pay me to do more techie work and if so it probably won't be through another company (so they won't be taking a cut) but this may mean me needing to negotiate my own price. I know what the beeb are paying for me at the moment and it quite scares me so I'm not sure I would feel comfortable asking for that much. On the other hand I know it is a fraction of what Domino charged for a day of my labour. That of course did have other overheads and in this case the Beeb give my computer, desk, etc...

So, anybody who has knowledge or experience able to fill me in with a few figures of what is reasonable? Much appreciated. :)