materials are usually about the same, most of the time you save on labor. i have seen companies charge the same either way but its usually about a 10% savings when we do pex, but then again its been so long since we have done copper i doubt i could be very accurate. also i see you're in michigan and for cold enviroments I would only have pex because it doesnt split like copper when frozen, it just expands. Conductor, do they really lower the value of a house in your area if it has pex? if so that is ridiculous, as for my area, western NC, they dont decrease the value any for pex.