I'm going to meet with the owner of the local vape shop who liked my 1590G build, now that I have my second one done, the 1590A, I'm going to have a sit down with him, let him play with them while connected to my laptop and talk coin about building some for him. I have my doubts he'll want to pay what I would have to charge. There are mods out there now with the 200 that I'm sure he could buy at wholesale less then what I would charge, but I'm not going to do all that work for peanuts.
Not going to tell you how to run a potential business, but I suggest sticking to your guns. Don't undersell yourself. You'll likely lose some business, but your time and work are worth money. If they like it enough, they will pay it. I used to do some really slick work on 360 controllers (modified buttons and custom artwork on the shell), and they weren't cheap. Probably could've sold many more if I lowered the price, but I was already not earning minimum wage, and anything less didn't feel worth it to me.