looking for a particular combination in a driver: longest throw, lowest price, robust, SQ not necessary

[Rik_bS]

its currently at the "vague concept" stage, but for option A) i would either be vibrating a dish of gallium with a laser reflected off it to produce cymatic patterns on the ceiling, or the same concept with a transparent dish and water or similar, with the laser refracting through.

Would you consider driving the laser with an audio signal directly, or are you seeking the chaos that the liquid will introduce?
There are a few options with using the ILDA interface of a laser, to drive directly with analogue signals (even straight audio!) or via some sort of transformation in either the analogue or digital realm
"Vector Synthesis" / "Oscilloscope Music" can be output via a laser, not just on an X/Y display... Here's some inspiration: https://www.instagram.com/_jestern_/

 

[mattstat]

a dish of gallium

A friend's children were into gallium for a while. They stained things around the house that you wouldn't think are stainable. With enough work, I think they got most of it straightened out, but it's something to be aware of if you're experimenting.

 

[weltersys]

my end-goal is a vertical representation of the music waveform in light, several metres high. . (glowing string) (i know i'm not going to get a nice audio spectrum with the highs at the top and the lows at the bottom.. but something dynamic and pretty should be achievable.

Most music exists above 30-60 Hz, the upper frequency range our eyesight can resolve into something that is not blurred.
A "glowing string" won't give much of a representation of the music waveform.