Train for a marathon...its free to train (outside), you can get solid guidance on the internet (from free websites), and it is a milestone in one's life. If your back hurts, try one of the exercise bikes, park it in front of the TV and make a pact with yourself: only can watch TV while sweating.
Another TV trick: when commercials start, commence push ups / sit ups /sets. It will make you hate commercials more, but it definitely keeps one from snacking while watching TV.
You can even do it with the PC: however much time you spend on the PC, break it up and use it as a reward. Let's say you can spend one hour on the PC today, before you even turn it on (or sit down), knock out some push ups / sit ups. Then every 15 minutes, hop out of the chair and crank out a set. That will motivate one to walk / play outside.
Take up a martial art if you want to spend money. I took Tae Kwon Do, and man that is a work out. If it isnt, then you are at the wrong do jang, find another. At the one I practiced at, the one and a half hour class always ended with pt and there literally was sweat dripping on the floor when we were done.
Personally, bikes are cool, but I dont see how that makes one loose weight, unless you have to push it.
By the by, everything you read in this post I have done, so it is not "advice", I know it works.
Cheers and good luck!