Debbie,
I have a Bosu and really like it. It came with one video, and then you can get a second video, "Absolutely Abs", for just s&h ($4.95). There was a thread a month or so back, I think it was "bosu on sale", where someone mentioned they had seen the bosu on a website for around $75.00 plus s&h. I bought mine at Sports Authority for $99.99.
I know very littel about the body dome; I haven't seen one in person. I know that the body dome comes with resistance bands. If you can remove them, then there's probably no real difference. If you can't remove them, then I think the bands would get in your way if you were doing cardio, or more advanced weight work.
Just my two cents!