I am sure you will get a bunch of differing opinions but ...
My take is that you should get a cheap one in the $100-200 range. You don't need fancy. After using cameras for my autoX the last 6 seasons my opinion is that the only thing a camera can teach is the relationship between driver input and car position. Of course that is a HUGE GIANT ULTRA MEGA IMPORTANT thing to learn but paying up for features that don't really improve on achieving that one goal are wasted money (unless the camera will have other uses in your life, then make a decision based on the sum of the camera's intended uses.)
PLEASEPLEASEPLEASE if you have only one, position the camera so that you can see yourself and a fair amount of the course in front of you, either high along the driver side B pillar or mounted behind your right shoulder. Bumper cams and roof cam angles are fun but are secondary or for entertainment, mainly because a viewer can't see the driver, which is the most important thing in the video! if it doesn't come with the right mount then Buy one that provides this viewing angle--when you show your videos to good drivers you will get useful actionable advice.
Edited to add: use your savings from the cheaper camera to attend a Phase One Evo school
http://www.evoschool.com
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Steve Carter
1972 Datsun 240Z-- resto pics at
http://picasaweb.google.com/srcartermd2007 GPW Honda S2000-- STR 86