Baz,
I have watched this thread from the start with some sceptisim for your comment as I believe it may be just to be to prevoke a reaction...
I will take your comment in good faith and give my input as not someone with a PPL but someone who is hopefully about to commence one.
If you think your finances preclude you from doing this solo then grouping up will not help - the whole lottery thing is as has been pointed out only going to help a few out of any that join and people will soon see this and leave - no matter what contract you have you will not be able to enforce the contract by commencing court action to recover money which is not there as funds will not be available which is why it would have commenced in the first place.
To not have your PPL is not to exclude you from the aviation community - do not be discouraged by the fact you cant afford to learn to fly just yet. Participating in any way you can will only further your knowledge until you can get to a position you can afford to learn and pass the exams. Getting a seat and observing is all good education, being able to ask questions and learn before approaching the PPL should stand you in good stead and in the meantime you will be having fun.
Whilst I agree in a preivious posters comment in that to sustain a PPL requires a degree of monetry fluidity - I also see alot on here whereby people are glad of the company when they have alot of flying to do - if you can get there to join them they will be glad of the company and all is good, whilst your not flying your able to learn and observe - whilst no monies may be asked for, contributions such as the cup of tea as thanks would be polite etc.
I myself wish to undertake a PPL course later this year and before doing so wished to at least experience a SEP flight to see if the whole solo engine plane (SEP) thing is something that wont scare me senseless (even tho I am pretty much adament I will be doing it). Someone on here has offered and I have graciously accepted to share a flight to give me that experience before I commit myself to the cost of the ppl - If I was going to do this through a flight school it would be sanitised and would cost alot more.
I would say from someone on the brink of signing on the dotted line to start the PPL trail - try finding the money to at least share a flight beforehand to make sure it is something your really wanting to do. I want to do it but have reservations as have never been in such a small plane. I have been told from people that have done it before a light plane is not everyones cup of tea - if you can get that flight and you love it - then I am sure you will be able to figure out what sacrifices you may need to make to fulfill your dream.
Hope you get there one day....