How far to travel while pregnant
I think there are two big things to consider when traveling during pregnancy.
The most important is: does your doctor feel it is safe to do so? During my pregnancy with Mason, I was asked not to leave a 2 hour radius of the hospital for the last 8 weeks. With the girls, I didn't have any limitations, and even flew to my parents' house 500 miles away at 36 weeks and came home at 37 weeks.
The second thing to consider is if you would feel comfortable delivering wherever you are traveling to... or somewhere inbetween if you are driving/taking a train or bus. You need to be sure you would be OK with either delivering your baby or seeing a doctor about complications no matter where you are and if you don't feel comfortable with it, I'd stay close enough to home that you'd be able to get to your doctor in a very timely manner - especially towards the end of your pregnancy.
With my son I traveled to Disney at 7 months pregnant. I had no issues whatsoever.