My First HD Camcorder

No new camcorder like this is available at the moment below $550.

The Canon HG10 ($615) might be the closest to what you're looking for, but I would highly recommmend paying a little more and getting its successor, the HG20, that is about to come out to get all the latest improvements in that department (I would also wait a little for the price to settle).

The cheapest Sony in that class is the SR10, and is available at $695.

You could also look at the refurbished/used market to get to that pricepoint, but those camcorders are currently huge leaps in PQ and features on each generation, so you would be compromising PQ/features for price.

I'm sure more than one here will question your requirement to get a HDD and gear you towards a flash-based camcorder. If that would be an option for you, you can look at the cheapest Panasonic AVCHD or the Canon HF100 that you can find available in the low $600s. Note that you'll also have to buy a flash card, but are getting pretty cheap right now.