Vandersteen Model 5, 5A were paired up some times with the QS MX-135 amps years back, and forward. Said to be "consequently, can be driven by a mid-power amplifier despite its modest sensitivity of 87db". Also helped by its built-in sub, etc. Worth looking into even if they are older and require some type of refresh, updates - considering the desired price range. As recommended, check with Johnny R.
I've seen MX-135s on sold years later at my local dealer, and discussion around driving various electrostat speakers there too. Some transformers in them, fwiw.