Good grief, you guys are making this into a science. You're supposed to be professionals, so there's no need to add replacement costs of goofed up projects. It's on you if you screw something up. That's why you charge the prices you charge..... for professional craftsmanship, not do it til ya get it right.
You basically figure out what all your overhead like insurances, utilities, mortgages/rent, a percentage of mistakes (not replacement costs), supplies, salaries, and miscellaneous & unseen possibilities and that becomes what you need an hour. Whether you are running a job that takes 4 hours on a screen press or 1/2 hour on the flatbed or 6 hours on the electric table, you charge out your hourly rate. Some things will yield better results than others and that's when you decide to keep certain areas in your shop or not. If you farm-out things, then that goes into your cost(s) of doing that particular project.
Now, if you find yourself doing a little of this and a little of that, then you need to either insert a shop minimum or drop that kinda work.
You wanna strive to become an assembly line and constantly banging this out or that, be it channel letters or digital prints.... and have multiple jobs going at once. When you hear all of your printers running and all your people are busy and your installer is begging for some time off, then you know that humming means you are making money.
If you get everything that comes in the door or over the internet, then your prices are too cheap. Time to raise them and trim off some more dead weight.
Work smart.