Hard to Hit all your requirements for <$500
Most camcorders create alot of noise via their mic inputs so synch in post is important for good sound, that said a mic>cam is better than just the built in mics.
I have a TM700 thats would fit your requirements, I have been considering selling it but it would probably be a little more than $500
Canon SX40 is a nice digital camera that has a mic input
TM700 does not record in SD 4:3, not sure what cameras do