Oops, I didn't pay attention to the monetary sign. Still, $600 for a pair of speakers should result in a decent pair of speakers. Just off the top of my head the
GR-Research AV/3's would come in under budget and should meet your needs. One of the
BAMTM variants may also fit your needs and will come in way under budget. Many people have reported good reviews of the
Tritrix. There are many more options - these are just three.
A few more questions -
Do you have preferences for any speakers types (sealed, ported, dipole, etc.)?
Have you heard any speakers that really impressed you (commercial or DIY)?
Do you use your sub when listening to music?
4 ohm or 8 ohm?