Apart from the condition of the aircraft, the biggest factor will be the number of people in the group.
£40,000 is probably a reasonable estimate for the total cost of an aircraft. So if you buy a 1/10th share, you might pay about £4000. On the other hand, you could buy a 1/2 share for about £20,000.
1/10th shares in this type of aircraft aren't all that common but they are available. Groups this big tend to form around much slower aircraft which are good for pootling around the local area for an hour or two, but which you wouldn't want to go touring in.
If you buy a share in an aircraft which is capable of touring (which the PA28 and C172 both are, although they're not the best choice of touring aircraft), you have to expect some of the members to want to take the aircraft away for a whole day at a time, if not longer - even if you don't. So availability with a group this big would probably be quite poor. A group of 4-6 people would probably be reasonable, giving you a cost of about £8000.
FFF
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