Cheep share doesn't always = cheep flying. Most costs will be similar whichever share you go for. There will always be hangarage, insurance and beaurocracy to pay for at roughly the same rate regardless which share you buy.
The way you can make a difference is to see how you pay (eg low annual useage - you may want to pay a higher hourly rate in return for lower monthly fees and visa versa). Fuel useage can make a big difference for example some VW powered aircraft burn 5-6 litres an hour, others can be up to 18 litres an hour. That makes almost a 3-fold difference in direct operating costs for an aircraft whcih may have looked cheep at the outset. It is also worth checking how much funding the group have in their kitty for when times get hard (I have never known anybody to ask though) and who does their maintenance.
Good luck with your search!