Machinable Wax, Foam, etc.

Crew:

I'm starting to design and build my Z-axis quill feed. This is on a 9x42
Bridgeport clone. I suspect it'll take some trial and error due to the
irregular shape of the head castings. I hate to start off with expensive
pieces of metal which leads to my qustion.

What materials are available for proofing CNC programs at a lower
material cost than aluminum/steel? I've heard of machinable wax and
machinable foam but have not worked with either. Can anyone relate their
experiences using these? Would a hardwood be usable? What are the
relative costs of the options? Also, does anyone know of sources for
smaller pieces of these materials? By smaller I mean 1" or 2" by 6" to
12" by a foot or two.

Thank you for your help. :-)

Hugh Currin
Klamath Falls, OR