Most of the hotels in Southampton are charging, double or tripple their usual room rates. I would suggest trying a hotel outside of Southampton and commuting in, the trains are very good and the station near the show. It is interesting that many hotels still have rooms available for the week of the show so maybe an indication that visitor numbers will be down this year.
Ibis is probably the closest and were I stay in Southampton, their normal rate is £50, next week it starts at £160 without breakfast.
http://www.accorhotels.com/gb/hotel-...re/index.shtml