There are opportunities to exercise at no cost in time. I usually bike to work and to go into town, which takes no longer than driving, and the harder I ride, the less time it takes. I walk up four stories to my office, which takes no longer than the lifts, and I'm usually up and down those stairs 2 or 3 times in a day. I play taiko, which is great fun, but is also pretty strenuous. So that's 7 miles of biking and around 100 vertical feet of stair-climbing every working day, and a cardiac workout of a few hours a week, for free.
There are other things I do, but these are the ones that effectively take neither time nor money to do.
I have a semi-recumbant exercise bike that allows me to work while exercising. It's not terribly expensive to get something to put a laptop on while using a treadmill or bike.
The question is - am I doing enough exercise?
I intend to provide a worked example for you to work alongside with your own calculations and decide if you should increase or decrease your exercise.
The benefits of physical activity are various and this calculation can be done for one or all of them; some of them include: