Airbase are on par with Sussex in regards to price on training in a Cessna...although the membership is cheaper (£65). Airbase has plenty of fly outs...and encourage cost sharing quite a lot.
Have a look around all the clubs at Shoreham though as it seems you are looking for a club to be a club rather than training...so see where you feal comfy!
Your spoilt for choice at Shoreham!