Does the place you live have walls? Are there large vertical beams of wood inside of these walls? If so, get a wall mounted pull up bar.
I have this in my garage and it is awesome http://www.amazon.com/Ultimate-Body-Press-Mounted-Gymnastic/dp/B003TYHTIA/ref=sr_1_1?ie=UTF8&qid=1350832963&sr=8-1&keywords=pull+up+bar+rings
You can do a ton of body weight stuff with the rings. If your wall studs are 16" apart it will work.