There are plenty of groups that have tried to run a Chipmunk without realising it is not a cheap aeroplane to maintain. I don't know why that should be, as Chippy costs are well known - maybe there are a some dreamers out there who think it can be done cheaply?
You have to realise this is a military aeroplane not designed for cheap maintenance, it is a classic for which some parts are becoming expensive (read:rare). Well run groups budget for all of this and buy up likely spares as and when they become available so they are 'in stock' for when needed.
A big bill for an engine rebuild (or replacement with a zero-timed unit) does not usually come as a surprise.
You can run a very big group around a Chipmunk because unlike a tourer, it isn't going to be taken away from base for long so diary slots can be plentiful despite the number of shareholders. A couple of hours and it's often back for the next member; even if it goes to a fly-in usually 2 members share the flight and it's only away for a day. The high utilisation in such a group keeps flying costs down.
A big group, so long as it is well run by folk who know the aeroplane well, is a great one to join. Guess how I know!