Hi the Royal Norfolk hotel in Paddington is good. Its right by the station. Rooms are basic,but easily within your budget. The breakfast is English or continental and its attached to a pub which cooks food. It takes approximately 10 minutes on the tube to get to Piccadilly. http://www.royalnorfolkhotel.co.uk

Hi,
I was working last year down in London, and we stayed at the Waterloo Hotel which is opposite the main line station. The accommodation was a bit basic, but I believe it has since been upgraded. The pub downstairs was brilliant, and very busy, must have been the World Cup, I believe England were participating!!!
The breakfast was great, from the full fry-up to something a bit healthier, and the location was great, a few minutes by tube from the city centre. If you Google Wellington Hotel Waterloo, look at the second down, or the fifth down, they will give you a bit more information.