I had the same difficulties when I tried to schedule my externships. What a huge headache. I agree it is truly a situation that will limit your externship opportunities. I ended up with a guy in NYC, but he swore that he was NEVER going to enter that situation again because of the headache. My price ended up climbing and climbing and I think that the final figure was about $2200, but I had significantly less coming in at 25000/75000 policy through my school.
I think that one wholesale company that may beable to direct you is Shand Morahan. That is where I started...but not who I ulitmately ended with 2/2 location issues. That too was limited because I live in Texas but was going to MO and NYC so the person that wrote the policy has to be certified to write a policy valid in all those places.
In addition to trying to find a policy, I would rec. approaching your dean...possibly as a group who are in the same situation. I think that there was a strong movement at my med school in the class following me to try to change the situation.
Good luck. I know that it tough. I do rec working through it and making the sacrifice...it maybe worth it in the end and then 800 dollars is just a drop in the bucket. Vandy is a great program with wonderful facilities...at least that is what I gathered on my interview.