welp.... for 50.00 you won't get anything exciting... I'll tell ya that. I have Dual 6x9 in my car right now.. but that's with a whole new stereo setup. I know DUAL isn't the greatest brand but it is in your price range and can be found at HH Gregg or Best Buy. Listen to them yourself before you buy them though, you may or may not like them. I only got them b/c they were cheap and provided some highs in the rear so that I wouldn't have as much "rear fill." Remember you only hear about 20% of the sound from the rear speakers. The other 80% is coming from the doors/front speakers.
Btw, my setup. Pioneer Premier 960mp, 2 12" Infinity Kappa Perfect 12DVC, DUAL 6x9 and Alpine Type-X 177A components in the front.