Travel insurance

I’m heading off this fall for a vacation that includes at least 10 days in remote stretches of Africa. For this reason, I’m going to buy a travel insurance policy that includes medical coverage.

However, I’m really not clear on what sort of coverage limits are reasonable and what is simply excessive. For example, one policy I’m looking at has a $200,000 limit on medical evacuation, another has a $1,000,000 limit, and along with it a higher cost for the additional coverage.

So my question is: can anyone point me to a resource that provides advice on how much coverage for travel in undeveloped places? The only websites I can find are for companies actually selling the insurance, and my searches of Lonely Planet, for example, have so far been fruitless.