Actually, the most cost effective, is basic common sense. Less calories in, more calories spent.
PM me, I work for a "diet food" manufacturer.
I too am on a "diet" for Disney, Sept/Oct. I have probably 25-30 pounds to lose. I purchased P90X workout with Tony Horton (committ to exercise 90 days) and Sunday will be 2 weeks, and I'm already down 2 sizes. You increase your water, I'm drinking close to a gallon a day now. Cardio...NOT high impact, you want LOW, FAT BURNING IMPACT (high burns calories, low burns fat) and weight training. He says wgt training every other day, but I do it everyday, along with the 100 ab ripper routine.
Meals: replacing my 3 meals per day to 5...hard! Eat within the 1st hour of waking up to burn the most calories per day. Breakfast for me is typically, 1 cup fresh berries, 1 banana, 1 cup fat free plain Stoneyfield yogurt and ice in the blender. NO added sugar, only what's naturally in the fruit. I drink it on the way to daycare/work.
Snack #1 (about 2 hours after your breakfast). Anything to crunch on. A handful of raw almonds, or 6 celery sticks with NATURAL peanut butter, (you'll need to keep it in the fridge, it's runny and since no pres. can go rancid).
Lunch: Whole wheat pita with organic dijon mustard, spinach and tuna-hard boiled egg white moisted with olive oil. Stuff pita and finish with an apple (you can add the Nat. PB for added protein).
Snack # 2 - same as above for me.
Dinner: Zucch./yellow squash, mushrooms, tomatoes, spinach and 1/2 a serving (1/2 a deck of cards) of chicken, then I put it all in a veggie wrap with FF cheese and pop it in the George Foreman.
His rule is to stop eating 3 hours before you'd go to bed, so for me, I need something fast and done by 6pm (EST). There are many varieties of snacks and meals, but this is what I can make from memory in 2 weeks.
Protein is really important when wgt. training too, it helps with your muscle recovery. Try to limit your sugar and carbs, you know the "white" carbs, whole grain is good, and I hate veggies, but have grown to like them in 2 weeks. It took my taste buds some getting used to, but it's doable. How weight? I'm down about 14 pounds now, and it's not water because my H20 intake has increased 100 fold!
Good luck!