One 4.1 teensy makes a pretty good synth

Why not 2 or 5? The cost is prohibitive but compared to processional made synths it is still cheap. Dirt Cheap.

Up to 4 could be hooked to a 5th in is2 master mode.

The would be 2 voices per teensy and a 5th for effects.

Or I could split them up between two total.

Many people have inputs and a display running on a cheaper esp32. I could still do that. The esp32 does have a i2s output so it could potentially output some basic oscillators.
It is also smart to not have the display not running on a micro controller that outputs to a dac as it can introduce noise.

Anyway teensy 4.1 + teensy 4.1 + dac + memchips= ~$65-70
$10-30 for a large screen
$9 esp32
$20-30 knobs and whatnots
case and panel $15
usb power bank. $20

Computers can do a lot but a dedicated hardware soft synth has some appeal.
All the other costs remain basically static as the cost of micro controllers go up.
85 for parts and 55 for teensy plus dac or 85 for parts and 150 for 5 teensy.
It would be worth it if I actually got a synth that was worth it.

It seems like I need to make a mono synth that runs on 50% cpu of teensy and sounds great. Then I multiply it by 4.

Easy as pie, right? (laughs in vaporware)
It will just take a few days. (100 hours later)