It is definitely an investment to lose weight and keep it off! I would really only suggest slimfast if convenience was the biggest priority for you. I'm not a morning person, so I grab one and run out the door in the morning and that works for me. But there are tons of alternatives out there that don't have the price tag associated with them. Plus, I think some may help you stay full longer with a similar amount of calories/fat. Nevertheless, the slimfast website has a lot of really good lunch and dinner recipes that I have incorporated into my usual rotation. If you do decide to try the slimfast diet, the cheapest option (that I have learned from this post!) is to go with the powders which I found at sam's club and amazon.com. It does require a second of prep, but significantly cheaper and w/o any metallic taste!
Find some food choices that you enjoy and can stick to for the long haul and I think you will be very successful. Good Luck!