Hey loulousw8, welcome to SW!! I also thought it was too good to be true, but I've now lost 51lb (3 stone 9lb) and can't believe how much food I can eat!! Admittedly, it hasn't been the fastest weight loss rate in the world, but in my opinion this is how it should be done! If I've learnt anything it's to be very patient! Some weeks I've been rewarded for my efforts, and some weeks I haven't, but the trick for me has been to keep going and eventually I have reaped the benefits! I've felt fab anyway because I've been eating healthily/upping my exercise a bit (in the form of walking mainly) so if I ever have a bad day or don't see the results I'd like on the scales, I just think what's the point in giving it all up, to go back to my previous weight and lifestyle- no thanks!!
In terms of cost, it can be expensive buying so much fresh fruit and veg, lean cuts of meat, healthy extra cereal bars etc etc, but it doesn't have to be! There are many cost effective ways of buying, such as buying things in bulk like pasta, rice, potatoes, a whole salmon and getting them to fillet it at the fish counter ( cheaper than buying individual fillets), buying cheaper cuts of meat for example I recently bought a ham hock for £2 in my local market and you can use it to make sandwiches, soups like pea & ham, salads etc etc. Also look out for bargains and special offers at supermarkets- keep eye out for useful threads on here like
http://www.minimins.com/slimming-world/40089-where-bargains-anything-else-thats-useful.html. I find that buying supermarket brand versions of things saves a lot of money! I'm going through a Weetabix phase at the moment, and the other day I picked up a box of 48 of Lidls own 'Bixies' for £1.29. Also cooking in bulk and freezing things helps your money go a long way! The key is being organised!
All the best at your first WI and I really hope you enjoy SW!! It's just healthy eating with a structure to it really!!X