High efficiency is part of the equation. You will also want to think about your speaker's impedance curve. Some high efficiency speakers with wild impedance swings can still be a problem for many tube amps. Also, your music preference, listening volumes, and room size all play a part in your thinking. Some will tell you that SET designs, especially 300b base designs, render music with an unequalled beauty. At ~3K, you are almost at the point of thinking about something like a Coincident Frankenstein used. Is that or a similar amp going to do it for you? If you listen to acoustic music with modest dynamics at low volumes in a small room, an amp like that could work for you. If you listen to Wagner operas and Mahler symphonies in a 3600 cubic foot room at realistic volumes then such an amp is certainly not appropriate.
Personally, I'd stay away from low budget amps. Most tube amps can't really deliver the goods without high quality transformers, and those don't come cheap. If you go OTL, like an Atma-Sphere S-30, watch out for that impedance curve. You should be able to pick up a used one easily for under 3K. The M-60's, even used, are going to be out of your price range.
Personally, I'd stay away from low budget amps. Most tube amps can't really deliver the goods without high quality transformers, and those don't come cheap. If you go OTL, like an Atma-Sphere S-30, watch out for that impedance curve. You should be able to pick up a used one easily for under 3K. The M-60's, even used, are going to be out of your price range.