Thanks Pete & Ray for your very helpful feedback! This really helped me in narrow down the options...
Ray, it sounds like the 6M or even the Max-7 might be just what I am looking for. Could you tell me specifically which model of the 6M you are using (maybe there is a link in Ebay from which I could order one)? And also, I was wondering... what is your take on the Max-7? From what I read it seems to be an improved version of the ublox-6, but I don't have either so I'm not sure if this is the case...