I would charge them for the paper, plates etc at the standard rate (purchase price plus surcharge) and charge the printing hours at a reasonable level. I don’t what how high that might be in the States, but in The Netherlands I explain to letterpress printers that a mechanic for your car would charge about 60?/hour, only for labor. I believe a letterpress printer should use more or less the same level.
Don’t worry about the final selling price by he designer. That is his/her issue, not yours.
Christiaan / passion for paper