Its not just about finding a school that can offer 152's for cheaper hourly flying - you have to be within close driving distance of it too. I live 5 minutes from thruxton which only operates PA28s. Popham is my next closest but does not offer the PPL. My next closest training school is an extra 15 to 20 mins away (and im not even sure they operate 152s). Take in to account the extra cost of fuel getting there over 6 months and you probably negate the benefit of training in a 152!
Steve