Best skiinny floorstanders

If you like that immersive experience, I would look seriously as Sansonic.  The MB5 B is going to be thin with great bass response.  The MB6 B will be taller and you may find it visually less appealing.  Both will be in your price range.  

Another interesting option is the Audiovector R3s.  Read Andrew Quint's review in the Absolute Sound.  They are tremendous and relatively easy to drive, as are the Scansonics.  

Full disclosure, I am a Scansonic Raidho dealer and I continue to flirt with Audiovector.  They are both awesome lines.  

Spendor A-line, Graham LS5/9f, ProAc, and any of these might work out well:  

https://www.usaudiomart.com/details/649719782-vienna-acoustics-beethoven-baby-grand-symphony-edition...

https://www.usaudiomart.com/details/649598483-kudos-super-20as-in-special-tineo-wood-finish-in-facto...

https://www.usaudiomart.com/details/649661844-raidho-xt-2-speakers-mint-condition/

https://www.audiogon.com/listings/lisa975d-marten-design-django-l-speaker

https://www.audiogon.com/listings/lis9jid9-sonus-faber-olympica-iii-full-range

https://www.audiogon.com/listings/lis9fc22-sonus-faber-olympica-iii-walnut-color-full-range

Big Plus 1 for Magico A3’s. Full transparency / I’m selling mine to move up to the A5’s under the category more is better. Right in the middle of your price point and as new. 

In a room that size skinny floorstanders are not the answer you need a large baffle full range speaker to project a full sound with enough volume and presence especially when you through in an eclectic mix of music a skinny floorstander will not do an 18 by 30 room well at all.

I think Audiovector R 3 Arreté is worth a look, especially coming from an electrostatic. Extremely fast and clean while being balanced and musical. I would call it neither warm nor lean, but rather quite neutral, which will make it somewhat sensitive to amplification matching - you will really hear which way the amp leans. Plays much bigger than its diminutive size as well, but is easy to integrate (works well close to the back wall). The review in TAS is quite complimentary and it was made an Editor’s Choice, but I think their evaluation only scratches at the surface of the speaker’s capability. (I am admittedly a bit of an Audiovector evangelist given I have made them my reference speakers but have no business interests whatsoever, I bought them from a retailer like everyone else.)