I'm scoping a print project that will include one red PMS and black. I'm thinking the print job will be less expensive than a 4C process because there are less plates of color involved. I wanted to add a 3rd color: a 50% tint of black (grey) — will this require a third plate and thus increase the cost of my printing?
If you are printing for example on a sheeted offset, you can use simply a screen. You can print photos or whatever.
You can inclusive print red over the black. That is a duotone.
It will be cheaper only if the print house is using just one or two head machine.
If they are using a 4 head machine its probably that the cost will be the same as cmyk. Probably just a bit cheaper.
On some processes like silk print, there is a chance that the halftone is too rough and not uniform.
On digital printing the cost will be the same.