Acme Thread- opinions?

OK, some rank beginner questions, to break up the "monotony" of all
these E=MC2 topics. ;')

I've ordered an XY mill/drill table from Enco and have some 150 oz-in
steppers to bolt on it. I still need something for the Z axis, best bet
seems to be for me to build it myself. The hardest materials I'm likely
to work in this are plexiglass and wood.

A local nut and bolt store (Tacoma Screw- really, it isn't a put-down)
gave me a price on Acme threaded rod of $13 a foot for 1/2 inch 10tpi,
and $6.50 for the "nut". Is that good, or bad? What kind of questions
should I ask to make sure this is better than the average carjack Acme
thread? For instance, should the nut be bronze or some other specific
metal?

I have been following the more advanced discussions with great interest,
if little comprehension. The basics of CNC seem pretty transparent, it
is the details that get hairy.

Thanks,
Steve Greenfield