Reasons for using no conductor finish on PCB
Simple, low-cost circuits and where the order is so big that it can be grouped with itself?

It sounds like you're assuming that it raises the price because it can't be grouped rather than actually knowing that as a fact. I could be wrong, but I'm pretty sure PCB fabs don't group multiple commercial orders together.

I also don't think surface smoothness is the objective because where surface roughness matters, oxidation also matters so you would go with ENIG.