Thunderroad

I've read the car rental threads here but could still use some advice. Basically, my wife and I plan to go to Campeche, Merida and Celestun next February. If we can work out the flights, we might even rent one in Campeche and return it in Merida, or vice versa. I have a few questions:

1. Aside from the fact that it looks like it would cost us about $100 extra for 10 days (at the Europcar site) to rent in one city and return in another ($370, versus same city pick-up and return), is there any reason we wouldn't want to do that?
2. Any particular rental companies to use or avoid?
3. It looks like the extra insurance charges would more than double a ten-day rental (again, based on the Europcar site) from about $370 (renting in Campeche and returning in Merida) to about $780. From what I've read, I assume that we want to load up on insurance. But any way to lessen the costs or any company that's less expensive re insurance but still reliable?
4. If in fact the $780 is the best we could do re car rental, might we be better off just doing hotel cars and taxis to get from place to place and to sight-see?

Of course, any other advice is more than welcome. Thanks!