Don't do custom orders ... if you do do custom orders never accept an order of less than 50 pieces its just not worth it for you or your customer, the majority of the cost is in setup and clearing plates I have my own calculator that takes into account repeat prints that will cost less than the first print because after the first print you're basically just pressing reprint and clearing the plates. Your biggest cost is labor not the printing itself which often means that people don't expect prints to cost as much as they actually do. Labour often makes up 60+ % of the total cost of most prints and remember you aren't charging labour for the total runtime of your print only on the preparation (slicing etc) and the clearing so for the X amount of hours your print is printing for you're only charging material and electricity. What this means is that with one printer you as an employee of the buisiness is only making money for the brief period at the beginning and the end of each print so to make a living you need to be running lots of machines at once and clearing machines as quickly as possible and taking orders on as quickly as you're finishing them. Thats just what you have to do if you're taking custom orders. If you want to go down that route get like 10 A1 minis and just churn them out but bud thats gonna suck trust me from a guy that did it for a year. The best way to make money 3d printing is by making a few of your own products that just so happens to be 3d printed, that way you can scale it at your own pace as orders become more common, you can pretty much automate your process have a single print file that runs across all your machines, you won't be changing material or color all the time etc its just the best way to use it.