My advice probably isn't worth much, but I changed my diet and lifestyle about five years ago after reaching almost 200 lbs. I've dropped 35-40 lbs., and I'd be happy to share with you how I did it. It's not impossible, and you might save some money instead of blowing it on a gym membership.
First, cut the junk food down to an absolute minimum, especially at first. Once you achieve a healthy weight, sweets and fats in moderation are fine. But until then, cut out all fast food, and start buying healthier foods (whole grain breads, pastas, etc.). Replace sweets with fruit. My food intake in a given day starts with a banana and Cliff bar for breakfast, a light lunch consisting of cheese, nuts, and fruit, and for dinner, usually whole wheat pasta, or lean meat once in a while with boiled veggies (carrots, and maybe a few potatoes). I eat as much natural foods as possible.
Second, start exercising. Buy three free weights: two ten pounds, and one twenty pound. Begin doing curls, and butterflies. If you're able to, start walking every day (for at least a half hour before your big meal of the day). I was a smoker for years, and had never been a runner. And once I started shedding the pounds, I decided to start running. Now, I can run 4 miles flat without stopping, and I'm averaging about a mile in 7.5 minutes. You would need to lose more weight though before trying running. But the walking and weight lifting will burn calories. Try doing crunches as well: tiny sit ups where you bring your fingers to the tips of your knees.
Third, be motivated and consistent. I'd say 90% of the struggle is willpower. If you can get into a routine, and make up your mind, the rest is easy.
I can give you some more pointers as time goes by, but these steps are not at all difficult, and could save you a lot of money.