This is my current setup, works well with my pretty shitty webcam.

Should do well with your C920.

Lights - I've seen them be as low as $20 before...

Softbox/Diffuser - These fit over the entire shell/housing of the bulb in the lamp above. Makes getting blasted by light a bit more bearable as it's much softer.

The lights won't get hot enough to burn or melt the Softbox. I've had them on for 8+hrs and they were fine.

Here's a picture of my setup when I stream. The lights look a lot brighter in here than I remember, so if you're worried about that maybe think about different bulbs instead of the ones that come with the Lamps.