I've matched a pair of M3s with a Veloydyne CT10, a DIY kit Vance Dickason Titanic 15", and Klipsch LF10. The M3s are very easy to coordinate with a decent sub.

In your price range, I'd look at Hsu, Velodyne, SVS.

The combo of M3s with a decent sub is something I assure you, you will love.

Enjoy the Music. Trust your ears. Laugh at Folks Who Claim to Know it All.