If you cant afford the gym buy three items:
1) Pull-up doorbar http://www.amazon.com/Sova-Therapy-Chin-up-Pull-Doorway/dp/B000RK0R92
3) Ab Roller http://www.amazon.com/AB-Roller-Double-Wheel-Ab/dp/B000VH3Z8Q
And perform the following excersize for 45 minutes a day, performing as many reps as you can for each 5-minute interval:
1) Push-ups.
2) Crunches.
3) Hindu Squats.
4) Ab rolls.
5) Pull-ups.
6) Kip-ups.
7) Hanging nail.
8) Dips.
9) Finish by Jumping Rope.
Trust me, if you bust it for as many reps as you can manage in each 5 minute interval (time it) you will be BURNT by the time you are done. Those hindu squats will ruin the toughest man. Remember the 10% rule: Each workout work till muscle failure, then the next week add 10%. You must constantly challenge your ability. Good luck!