A quick
aliexpress.com search reveals 5K ohm pots (with mounting nuts) are
$10 for 50 (free shipping in 12-20 days)
$2.16 for 10 or
$1.30 for 5 (free shipping in 20-39 days)
The minimum cost of the parts for one Auduino Synth, not including the Arduino, are about $1 for the five pots, when bought in lots of 50 (each $10 order makes 10 Auduinos). Plus wire and solder.
What would really transform this type of project into something valuable to the public would be some sort of Arduino shield. Otherwise, even after people solder wires to 5 pots, they still have to find some solution to connect them all to power pins on the Arduino, and they'd still be left with a messy project whose wires could easily pop out of the Arduino in transit. If people could solder 5 pots to a board (doesn't have to be a PCB- it could just be perfboard or stripboard) we layout ahead of time, using a few jumpers and a few pins to Analog ins and power, they could easily get an Arduino later and program it with the code. So, designing some sort of shield for the pots would be a way to offer a class/workshop, whereby people don't even need to have an Arduino there with them, with the option to come back with one on a Tuesday and program it. We could pre-program some Diavolinos and sell some of our stock of Arduinos, without feeling like we'd need to stock up on more for an Auduino project. We could just design a shield layout, get some perfboards/stripboards, maybe design a PCB, and order some bulk pots. Separate them into kits, make printout with a wiring diagram and the code download link, and offer to help them solder their kits up.