Wright 2A3 monos should be in your ballpark and are exremely good. The ASL Tulip is also very good and is less money. I personally prefer the 2A3 tube to the 300B, but you do have significantly less power. I suggest these because you asked for "low power set". If you are willing to try push-pull tubes I can heartily recommend Quicksilver mini-monos. They are definitely in your budget new and can be had very inexpensively used. 25 watts per channel, very reliable, and close to set sound.
