A mere £110 pp?! It can and does often cost more, and with eight or more places per balloon then they'll want to fill it to make a profit. They'll be operating to an AOC with all attendant costs, it's not like renting a C152 from your local club!!!!
There are many ballooning outfits you can search for, plus does the British Ballooning Club (sorry forgotten their actual name) have a website link to operators?