There are loads of cheap places around Victoria station. Many of them are listed on the excellent Hostelworld website. (Don't be put off by the word 'hostel' in the site name; it also lists cheap hotels and B&Bs. Just use the 'additional search options', selecting both 'Budget hotels' and 'Guesthouses').
Where a sufficient number of people have recently reported on an hotel, the results page will show a percentage satisfaction score. However, even those hotels with no scores shown often have reviews which you can read. Just click on the hotel details and then on the 'Reviews' tab.
http://www.hostelworld.com/
Chris