Sensitive enough speakers for low power SET

Second the Coincident. Several advantages to high efficiency speakers such as ease of load for the amp and oft very good low volume level resolution.

WLM

I am not sure about prices in the USA, but the WLM Gran Viola MkII might just fit your budget (unless the exchange rates wreaked havoc). Otherwise look at the Lyra MkII or Aura. These are ingenious speaker systems that can be upgraded (see the "Super-Pac" option) and adjusted to fit just about every room, and ... 97-98 db 1W/1m is standard at WLM.
http://www.wlm-loudspeakers.com/indexengl.html

Besides of WLM, I second Zu (whereby, I only know the less expensive Druid MkIV myself)

Good Luck

I have Zu Definition 2s and have heard Audio Note speakers. Both are SET friendly.

Klipsch

I have Klipschorns (104db) and just got an 807-based SE amp @ 6 watts/channel from a builder in the Chicago area. I'm in a small room, but with 6 watts I could be in a large room and still have plenty power. I had a SE amp with EL84s @ about 2 watts and that was about enough in a small room.

For what it's worth - I made the move to low power / Hi efficiency a couple of months ago and I don't think I'll ever go back to higher power stuff again. This 807 amp / KHorn combo is the best I've ever had in my room by far.