I was in Bonn a couple years ago. I stayed there for two months after four months in Koblenz. I can't remember the name of the village/suburb where I lived but it was a good ways up the Rhine (i.e. south) from the city on the east bank of the river. I had no car so my exploring was   a bit limited. I didn't really mind paying high prices since I was living in very cheap accomodations - much cheaper than I expected or wanted - the only furnished short term rental I could find in Koblenz was a basement room with a sink and two burners and a shared bathroom in the hall. But it worked out to about $200/mo so I was flush with cash.