Depends what you are looking for, are you taking children etc, but there is a new youth hostel near Lewes in the South Downes. I have booked a family room for a few days at half term and am hoping for success.
Oh Emma, thanks for that can you let me know what it was like please? My 16 yo DD will already be in London, doing a course but may want to spend a day/ night with us. Then we have our 12 yo DS who has Down syndrome, autism and PDA. He doesn't do crowds and noise, doesn't cope with hotels, cafes etc. hence why I also need self catering.