i don't believe in all the diets out there, it might work for some people but if you want to stay healthy it is better that you eat everything with moderation. that way you know that you are allowed to eat something and won't fall back in your old eating habits.
as for affording the gym thing maybe you should wait with that. start with eating right first (whatever diet you choose) so you get that right,(and under control) and can concentrate more. you will loose weight just by changing your diet. you can also walk everyday that is always good. then when you feel ready you can start the gym. if you haven't excercised regurlarly before you have to take it slow, so the body can adapt to the change and also so you won't feel that you can't handle it, find it boring and quit.