Are period homes more expensive to build than other styles?

Generally a home's interior finishes constitute the highest costs in relation to foundation, envelope, roof, or rough plumbing and electrical.
Period homes (before 1940) definitely have more trim work and moldings than a contemporary or modern design which is free of crown molding, paneling, elaborate ceiling treatments, etc.
Historical period homes were all dressed out by hand, as well as built by hand with no power tools even. Plaster moldings were set in the field or applied wet. Wood crowns were built up with several layers of running moldings and/or hand carved.
Modern plumbing fixtures, except for gold plated ones, can be equivalently priced unless reproductions are sought.
In today's market there are prefabricated moldings, medallions, brackets and other trim available in plaster, wood, and synthetic polystyrene, fiber reinforced plastic, etc. These items are considered 'big bang for the buck' expenses that help defray the high cost of on site hand built and placed trim work.
In general a period home will cost 1.5 to 2.0 times the cost of a contemporary home. ---Potentially more even as decisions on whether to specify real granite and marble columns versus cast concrete or fiberglass, limestone vs. porcelain, slate vs. concrete tile, are weighed.
See essay here: Boxy but Good! -- http://dreamhomedesignusa.com/boxy.htm