Hi Jim,
I have used the Von Schweikert VRS-1 and the Martin Logan Grotto which are both in your price range at least used. They have a small footprint with very big sound. Both of these subs are very quick and I found them musical. Hope you get some more good suggestions and find what you are looking for. I ended up buying the Martin Logan Grotto and still think it is a bargain about a year later.
I have used the Von Schweikert VRS-1 and the Martin Logan Grotto which are both in your price range at least used. They have a small footprint with very big sound. Both of these subs are very quick and I found them musical. Hope you get some more good suggestions and find what you are looking for. I ended up buying the Martin Logan Grotto and still think it is a bargain about a year later.