Well in case you are a bodybuilder then it is a different story, otherwise there are many things you can do to stay fit and avoid paying expensive gym membership. So before end up paying too much at your local gym, we recommend you read this!!!
Running
Running is the most basic and most effective cardiovascular exercise. The best thing about it its free. All you need is a pair of shoes and definitely will to wake up early in the morning and hit the road. In case you feel your neighborhood is too crowded then you are being lousy. To remain in shape finding a joggers park is not that difficult.
Just in case you haven't exercised for a long time, start with simple walk. Eventually increase your speed and start running against a timer.
Skipping

Tower Running

A good and effective start would be to avoid elevator and take staircases to your premises in normal daily routine. After a while you will increase your stamina and then you can climb against a timer. But make sure not touch the point of no return.
Cycling
Cycling is another cool thing to do. Although there are expensive cycles in the market. But there is cycle for every pocket. They start a at a little price of Rs. 4000 or if you want you can always find used ones as well.
Trekking

Well thats all from our side. Hope we have inspired you enough to keep you healthy.