Tom,

I think you already have something lined up, but for what it's worth:

Max-gain sells fiberglass products and has push up fiberglass masts that 
while not cheap, are  higher quality than others being sold to hams:


http://www.mgs4u.com/fiberglass-push-up-mast.htm
A different way to go is with surplus military 4 foot aluminum sections. 
   These don't telescope, but would have to be assembled and walked up 
from horizontal to vertical:

http://www.tmastco.com/

And one final source for junk as you engineer this project:

http://www.penningerradio.com/

73, Steve KW3A