The op mentioned that he needs 2 10 inch subs for $300 or less. This automatically excludes Alpine Type R slims and Image Dynamics IDQ/IDMAX, although I heard those are excellent subwoofers. For this given price, probably RE SE/X, Alpine Type-Rs and Dayton References HF are decent options. The type-rs have more linear xmax than Daytons and can be wired for a final 1ohm load, so I would speculate that they can get noticeably louder than Daytons. However, the Daytons HFs are more of pure SQ subwoofers with ultra low inductance and distortion, which had been measured, and with the help of car's cabin gain I suspect they should be able to produce far more sound than is necessary to blend with the front speakers. I personally would be very tempted to try the Daytons. RE SE/Xs are also decent subs, but their basic design hasn't changed for years, while the new Type-Rs are brand new subwoofers with many new changes for SQ and SPL, so I would be tempted to try them out instead of RE subs, even though RE SE and RE SE/X have excellent reputation as well. RE SE subs are known to have very good low end, but no output above sub bass frequencies making it harder to blend them with the front stage. I personally prefer 15 to 25% of midbass sound originating from the subwoofers, specially if you can time align them with the front speakers, resulting in better blending and fuller sound IMO, since an average 6.5 inch mid will not play midbass with the the kind of authority that I like.