avrodamo
As far as I know, you're not allowed to advertise for passengers on a PPL, even if you will be cost-sharing with those passengers. The only exception is if you advertise in a flying club, and both you and your passengers are members of that flying club.
Of course, it's a fairly thin line between advertising, and e-mailing a load of work-mates.
MattDavey
The cheapest way of hour-building in this country, as long as you've got some cash you can part with for a while, is to buy a share in an aircraft. As long as the aircraft is not new, it won't lose too much value over a short-ish period, so you'll get most of your money back. The exact hourly cost will depend largely on the type and condition of your aircraft, and also on how many hours per month you fly. You can fly for less than £15/hour in some single-seater aircraft - although you'll probably need lots of tail-wheel time first for most of these. I currently fly for about £25/hour wet and £50/month - that's also tail-wheel, but there is a trike version of the aircraft which would cost about the same to run.
However, if you're looking to get your ATPL(f) via the cheapest route possible, the best thing is to not worry about flying while you're doing your exams. Do your last 50-or-so hours after your exams, and then when you start your CPL you'll be far more current, and will find the higher standards required for the CPL less challenging.
(Of course, if you're anything like me, you won't be able to handle the idea of going a year or so without flying, because flying is just too much fun to not do!)
Everyone
If you guys manage to set up a study group, I'd be really interested to hear how it goes! My initial thoughts are that everyone studies at a different rate, depending mainly on how many other commitments you have, so I don't think it will work. But I'd love to be proved wrong!
FFF
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PS - Is it just me, or are there at least 3 different subjects now being discussed on one thread?
Scroggs/WWW - how difficult is it to split this into separate threads?