Just by using a regular rope for rope jumping. Some of us are on a budget. :P I can only think of one back exercise.
- Hang the rope over a bar (can be a pullup bar, or regular outdoors workout bar in a park).
- Grab the rope ends and let your body hang close to the ground with your legs in front of you, as if you were floating above ground with only your feet touching the ground. Keep your body tight and flat.
- Lift yourself up as much as you can if you were rowing.
- The lower the position, the harder the exercise.
Anyone has more ideas?