Okay since many of you guys are not giving concrete answers, I will since I am a filmmaker myself.
DSLR's:
-Ability to rack focus and create your subject isolated from others.
-Higher MP than most other cameras. Canons these days have 18mp or higher.
-Ability to switch out lenses to others such as ultra wide angle, fisheye, telephoto, medium telephoto, macro, etc...
-Ability to control your settings. Set the shutter speed, aperture (controls DOF), ISO, resolution, and fps.
The main thing is that you are saying that at a $300 budget, the quality on consumer cameras and DSLR's are very poor. You may be able to get a HD sony handycam for that money, but the settings and creativity are limited. If you are not going to use DSLR's for photography and cinematic videos and things like that, just go with a consumer camcorder and that will be fine. But if you are willing to pay the extra cash to get more of the customization and quality, dslr's are definitely worth it.