I do a bit of module-sleuthing from time to time, and when I add DIY modules, I tend to put the "worst case" price in...because while people HATE surprises like modules they thought were one price but they ACTUALLY come in at something higher, they do like it when things come in LOWER. It's sort of like "free money", psychologically. So if there's just a board and panel, I'll drop that price in, but I try to also note in the description that the price is for "PCB and panel only". However, getting users to all do the same sort of thing on that is like herding cats, so I just do what I do and hope it filters down somewhere.