[matt_the_bass]

The short answer is enough money that it is worth your time. You already have a job. Presumably you have a life outside of work. So this side project has to be worth giving up some of that outside of work life.

I know it’s not the same but I make word clocks[1]. They are limited edition and (I think) high build quality. I’ve found one brand of high end word clocks. Mine are a different design but at least equal finished quality. I charge on par with those. I don’t sell a ton, but I don’t spend a ton of time. The time I do spend on selling works out to a high enough hourly rate that it’s worth it to me to give up other activities (ie opportunity cost).

1. Www.finewordclocks.com