Most “disappeared” speakers.

Electrostats combined with a good sub - sublime. 

OB’s, aka Open Baffles, aka speakers w/o a box design. Combined with 2 subs and a low watt tube amp, very tough to beat for quality sound on a reasonable budget. 

Lx521. Sound field is wide and realistic 

In that price range new and used you have a lot of choices in vanishing speakers. I was lucky enough to find a pristine pair of Maggie 3.7, sent them back to Magnepan for a total refresh and they emerged as the lastest model the 3.7i all for less than $4K.
Just be aware that the more transparent a speaker is the more it will reveal the shortfalls in your sources and supporting equipment. 

The omega super alnico without any crossover is a nice choice for a disappearing speaker. 

With a sub and low watt single ended amp it is sublime. 

I have a set of Dahlquist DQ10s with two Dahlquist Subs, that I have upgraded here and there along the way  These speakers were always noted for their sound staging and disappearing. 

These speakers can even do sounds that can move around the room . . . even passing, in its illusion, right through your head. I bought them used back in the 80's and still have them today.