If you could direct me to a solid video DSLR under $400, that'd be great.
OP I have a Canon HF R300 that I got for $250 because I'm broke as fuck. It shoots good video and has decent manual settings. The screen is nice and big, and the autofocus is quick. For a mount, you could invest in a flycam with your leftover money. I know people talk shit but you're clearly not serious about filming and it would do just fine. You could always sell your shit to get nicer shit in the long run.
Video sample:
Coastal Stoke from Alex Forcillo on Vimeo.