Exersize question

Here is the situation.

I have about 4 more weeks in this splint, humerus is connected on the inside and there is a 5mm gap that is filling on the outside. I am now able to take the splint off to clean the arm, (thank you thank you thank you), and the atrophy is amazing. The right arm looks like it belongs on a vegetarian.

I was lifting and doing calisthenics a year and a half ago, and was feeling pretty good. Then the shoulders started to hurt and the lifting was cut on ciro's recommendation. He said that I could go lighter. I had every weight the wife has ever bought to store to safety gather dust, and the max was about 150#. I cut that in half for military presses. So I was already pretty light and doing lots of reps.
Then I blew out my knee in the summer (unrelated to workout, meniscus tear) and quit altogether.

I am thinking of a rowing machine. They are good cardio (needed) full body low impact which it seems that I need because things seem to get hurt more on me now without trying. I know I won't go to a gym, its not me. I can do the discipline part as long as I can't avoid seeing that I am not doing it, and I can bang it out in a 1/2-3/4 hour pre work.

Anyone have a rowing machine, of experience with home units. I am looking at decent models, not 40.00 specials or 1200.00+ gym equipment. It seems that I can get something ok for about 400.00