Member's recommendations for tube amplification

I don't know if that many SET amps will fit your profile.  While SET amps are, generally speaking, simple in design, they require really good, and expensive transformers (generally large, air-gapped transformers).  The tube type that fits the criteria you mentioned is pretty much limited to the 300B.  But, most of the 300B amps are on the warmer sounding side. 

The larger transmitter tubes (e.g., 845, 805, 211) run at quite high voltages which would make me very leery about any cheaply built amps.  Parallel output tubes in SET configuration is sometimes used to get a bit more power out of the lower-powered triodes, but, that turns out to be not that easy to implement. 

I think you will have the best luck looking at pushpull amps.  My own personal preference is amps running 6L6 tubes.  These put out less wattage than EL34s, 6550, KT-88, etc., but, to me, they sound sweet without being muddy or sluggish sounding.  A lot of lower-priced tube amps run EL84s; I like this tube too.  I generally like the amps offered by Synthesis (Italian) and Audio Note (UK). 

There are a lot of very old vintage amps that can be found in your price range, but, you would have to work with someone who knows, and can refurbish the old stuff. A refurbished RCA or Northern Electric 6L6 amp will blow away surprisingly expensive current offerings.  Other old brands, like Scott or Brooks, have really nice models too.

While I have, in this thread, cautioned against using the really low-powered triodes in single-ended topology, I am sort of in agreement with clio09 about the possibility that someone may be satisfied with the result; it all depends on the specifics, such as how easy a load the speaker is, type of music, how loud one listens, how large is the room, and most importantly, what compromises one is willing to make.  There is always compromises involved, no matter the budget or any other consideration.  If one does not highly prize extremely deep and tight bass, or if one listens mostly at modest volume levels, a SET amp might work even with speakers not designed to work well with this type of amplification.  Unless one listens to head-banging music most of the time, the average listening level will be such that one would be using less than a watt with even inefficient speakers.  So, the question is: how important to you is it that the sound system performs well for the comparatively shorter time it is asked to deliver higher volume?

When I listen to large choral works with my 6.5 watt parallel 2a3 SET (Audio Note Kageki) driving 99 db/w 8 ohm speakers, I can tell that on peaks, the sound is becoming a little bit muddled and is sounding compressed (not really getting much louder even though it should be).  But, for almost all other types of music, the amps deliver all the power I need, and given my priorities (I demand good dynamics and a full and lively sound at LOWER volume levels), the compromise is worthwhile.  The same holds with my other low-powered tube amps.