Digital BW, The Print

Does anybody care to print an occasional large format print, say about
20 x 30 or so, or possibly 16x24?  I have a client who may wish to order
one of my photos at a larger size than I can print on my 1280. If so,
how much would you charge for the service? It would be black and white,
on a good watercolor paper. 

Please Reply off list if you have any interest in printing the
occasional oversize print.

Thanks,

Jerry