I think all the points Rod1 makes are very sound.
I would add the following thoughts.
I suspect unscheduled maintenance (the nasty surprises) will depend greatly on the type and age of the aircraft. If you join a group operating something less usual and older expect large bills, and be even more carfeul to ensure it is in good condition before you join. Similarly if it is IFR capable, one has to suspect maintaining it in this condition, if that is the group's intention, will add to the cost. Finally think very hard about whether the group is professionally operated. Of course I do not mean someone is paid, but that there is a solid committee with agreed responsibilities. It is surprising just how much is involved - but getting this part right adds to safety, ensures maintenance is taken care of on time and with minimium delay, bills are paid, etc., etc. Ensure the group has some minimium currency requirements - this will help to ensure the aircraft is correctly operated which in turn will impact favourably on costs! Lastly, what about the engine fund / prop. fund - is it on schedule? A fund with an under provision or worse, no fund at all, will result in a very unpleasant surprise at some point for the members!
[This message has been edited by Fuji Abound (edited 03 July 2001).]