We have an older Canon HF10 which is great, although we haven't taken it to WDW yet. We have taken a Flip, though. Not only is the memory limited, but it's not good at shooting video in extreme conditions. One example is that we shot video of EE. In the dark parts, the video was black, then, when it went into the sunlight, the video went all white because the camera's exposure system couldn't adjust fast enough between dark and light. A good camera will be much better at doing this.
I just saw one of canon's HD cameras at costco for under $500. You can't go wrong with them.
Another option is to buy a DSLR that is also video capable. Nikon, Sony and Canon all have DSLRs that take HD video for around $500-700 with a lens. You'd be getting two devices in one which is not only cost effective but also reduces what you have to lug around.
Hopefully $450-700 fits your definition of not crazy expensive....