Aspect ratio converters?

[madlabs]

Man, am I out of my depth. I have been looking at all sorts of converters but none seem to mention 4:3 specifically. There seem to be a lot made by Black Magic in my price range but I have no idea what I need. Where is a good place to go school up?

My ideal would be a hardware solution under $150. All I wanna do is get rid of the dang side bars!