(I can only speak to the "helmet cam" part of your question)

Don't believe JVC has a good model for helmetcam use. Sony is the preferred choice (for a few reasons). Sonys also usually have a Lanc port - something you will want for a helmet camera. Unfortunatly, I don't know a model that meets your $400 target.

Here is a list of compatible camcorders for Helmet cam use.

Sargon

Xtreme Recall