I way under-estimated how long it would take to actually design something. I did a cost breakdown ahead of time on printing time + materials, but at that time the designs were simple, just text.
As things advanced, we had people ask for logos, and recreating them is really what took time.
There is still one lever here, and that was to increase the price to make that design time actually worth it. If I had to continue, that's what I would have done, but I was still losing my weekends and my free time was just more valuable.
Lots of places charge a separate fee for the design aspect like this. Printing prices will stay the same as the time + materials is consistent, so that's what you charge the client. However, since you're having to do the design part, that's where you come up with a different pricing scheme. I've been in multiple places that had similar concepts that kept things somewhat sane.