What are the best DSLR cameras for the lowest price?

Yup, I recommend one that I own, the Rebel XS = $ 500 with a lens.

For $ 500, I strongly recommend the Pentax K-x.
First and foremost, it shoots HD videos. There’s no
Canon camera that takes videos and costs under $ 600 with a lens.
The K-x also provides a high 4.7 frames per second shooting rate.

I would consider Pentax K-x Digital SLR Camera
* 12.4-megapixel CMOS sensor with Pentax Shake Reduction; HDR image capture
* Kit includes 18-55mm f/3.5-5.6 AL lens
* Capture widescreen HD 720p video at 24fps;
* 2.7-inch LCD with autofocus and Face Detection Live View
* 4.7fps capture rate with 1/6000 sec max shutter speed;
* 11-point wide-angle autofocus
* Powered by AA lithium batteries;