Exercising ideas?

So guys, I really want to get in shape. I'm sick of feeling flabby and lazy, and I know I can do better than this. In terms of diet, my house has much to offer because my mother is a health freak. Exercise? Not so much. We don't have any fitness equipment and I can't afford it, gym memberships are too expensive, I live on a national highway so I'm not allowed to walk or bike on the rode, and my yard is very hilly. I need some ideas as to how I can get substantial exercise without breaking the bank. Help?