It cracks me up that people spend so much time, money, and mental energy on staying fit. Hey, this is MMM; remember the "muscle over motor" blog post?
I've designed my life in a way that provides exercise as a side benefit with little or no extra investment of time and money required. I walk to work, which gives me a couple miles a day of light cardio (brisk walk with hills). I heat with wood, which involves a lot of cutting, splitting, loading, fetching, etc., and saves me a lot of dough to boot. I use a push mower to mow my hilly lawn. Rake leaves with an actual rake. And so on. Go for a hike if I have any spare time. I never, ever go to a gym or use any exercise equipment, and pretty much every day I find an opportunity to sweat and get sore. I'm no body builder or distance runner, but I'm in way better shape than most middle-aged American men.
You don't have to worry so much about whether you're working every muscle group just the right amount and in just the right way. Engage in a variety of physical activities, and you'll get a variety of exercise. Ease into an unfamiliar activity until you get the hang of it. If something hurts, stop doing it. The human body was designed to work for its supper - just use what you got.