You've already got some great candidates on your list, so I'll add a few more "off the radar" options that might be worth a look in your price range.
Sachs SP14 -- this is one I'm seriously considering myself. A big bonus is that I think they offer a brief in-home trial, which to my mind is huge. I know they offer balanced connections, but I don't know if it's fully balanced. Here's a link...
http://www.tubes4hifi.com/don.htm
A couple others would be the Backert Labs Rhumba (again not sure if fully balanced) and Linear Tube Audio microZOTL2.0, which looks to be single ended only. Just for some other options. Best of luck.
Sachs SP14 -- this is one I'm seriously considering myself. A big bonus is that I think they offer a brief in-home trial, which to my mind is huge. I know they offer balanced connections, but I don't know if it's fully balanced. Here's a link...
http://www.tubes4hifi.com/don.htm
A couple others would be the Backert Labs Rhumba (again not sure if fully balanced) and Linear Tube Audio microZOTL2.0, which looks to be single ended only. Just for some other options. Best of luck.