I had a good friend who had had lipo and a tummy tuck done. I can tell you she looked really great after all the healing, but getting there took a very long time. A few of the holes that the lipo had been done from refused to close up, and then resulted in hemotoma, it literally took some 6 months after the surgery for her to be fully healed. She said later it wasn't worth it; she liked the result but would have been happier not going through the whole ordeal.
I find it suspect that diet and exercise don't work for anyone. How many calories do you consume in a day? If you can't answer that you aren't dieting. The average adult needs no more than 2000 calories a day. Combine that with the proper workout and you WILL lose weight, but it takes a lot of work. Sit-ups don't do it, you have to do cardio 4-5 times a week for a half hour at least to actually burn fat. If you aren't currently doing that, you can't dismiss exercise as though it doesn't work for you.
I had considered, not too long after I had my son, to have a mini tummy tuck. But I found with the right work out regiment and watching what I eat, I don't need to surgically alter my body to get the result I want. Consider a gym membership, there are a lot of places that give you a personal trainer who can structure a work out routine specifically for you, and its a lot cheaper than surgery.