Lots of B&Bs around the Kings Road area (Ascot House mentioned above is decent for that sort of price) as it is near the conference centre. Our office is just opposite the conference centre and next to us is a lovely B&B called Brookfield House but I think it will cost a bit more.
Check that you aren't in the area at the time of a conference because if you are they will all be booked up and high rates.
For food – best Mexican: Salsa Posada just off Bower Road. Best Indian: Sartaj just off Kings Road. Best Chinese: Horoscope just off Cheltenham Mount. Then there are the chains (Pizza Express, Wagamama etc).
Best mid-price: The Tannin Level
Best expensive: Orchid Thai Fusion in Studley Hotel and William & Victoria's on Cold Bath Road (W&V's books up well in advance).
Best to avoid: Drum & Monkey seafood restaurant – used to be amazing but trades shit food on past reputation.