You would be looking at somewhere around £350/500 Euro's a week minimum in outer London and I wouldn't even bother with central London, if you have to ask how much, you can't afford it.
Plenty of companies have web pages. Your best bet is to Google and see what you can afford. If you see something you like I can always give you an idea of what the area is like and any transport issues.
Cleveland May 24 to June 4th 2007 - I came, I saw, I fucked off home again.