With a $500 budget, you might want to consider:
$176.12 Tascam DR-60D - better form factor than the Zooms, fits under your camera instead of taking up a shoe mount or hanging off your rig
$66.95 Rolling boom - for occasions when you're shooting solo
$15 Kindle copy of Ric Viers' The Location Sound Bible - investing in this book will save you a lot of time and money in the long run
I have the DR-60D - it's a great recorder - and mounting it below the camera makes a whole lot of sense.
For $500, this may be the best value for money setup you can buy.
Hope this is helpful and good luck!