I agree with Tim that Fritz is worth calling; he's a good guy, and the Carbon 7 is very nice indeed, if a bit over your stated price range. As Tvad points out, not clear that any of the speakers mentioned are esp. well suited to blues -- but I'm not sure a "blues specific" speaker is required (or if one exists). From what you've said, a more important issue might be what speaker does well at moderate volumes -- not all do.
John
John