Surround speakers

I see a used pair of Paradigm ADP-150 Dipoles here for $200

I can also recommend Definitive Technology and NHT if you can go up a little in price, but I don't see any dipoles here.

I also see a pair of Elan thp650ss dipoles in your price range, however I don't know anything about them, except they're listed as new.

Rich

You really should try and purchase surround speakers that are timbre matched to your main speakers and centre channel. This will almost always mean buying surround speakers from the same manufacturer as your main speakers using some of the same drivers as your main speakers. If you don't do this you will most likely end up getting an inconsistent sound when listening to 5.1 soundtracks and especially with hi-rez 5.1 music recordings.

first read 'Sound Reproduction' by Toole, then decide.