Hi parkerela,
Well, first things first - Lighter Life is the best thing I ever did - seriously daunting, but worth every shake, and every penny!
The cost for foundation (as laststraw said) is £66 per week... you aren't financially obligated to stay the fourteen weeks - although you are asked to sign a declaration to say you will... and I think you need to go into it with the attitude of seeing it through (the first 100 days at least) otherwise people leaving willy nilly can really upset the group dynamic of those that join together.
During route to management costs fall from about £40 something a week to about £15, depending how many meals you are substituting with foodpacks - this is done over a further three months - and this is the part of the programme that appears to mean the difference of long term success and a quick fix - therefore, I would definitely not consider doing Lighterlife unless you are in it for the long run.
Management is just 'living' afterwards. You have the choice to attend management counselling sessions - for free, only paying for your foodpacks if you need them for any reason. This is ongoing, and is there indefinitely if you need further support once you leave the 'programme'.
Hope this helps a bit, and if you decide to take the plunge, make sure you keep us all posted on your losses - it's pretty cool stuff

xx