I once asked for a custom shaped alu extrusion (rudder foil). The simple answer from a well known rigging supplier was: "You wan't pay it. Make it form glass or carbon fibres."
It works fine for standard shapes like tubes. We got 4m spin pole from 40mm alu for 150€ or so.

By the way, if you are close to a company working with CFRP, you may ask for cutting scrap (or however it is called in english) or expired prepregs. Sometimes you get it for free.

Cheers,

Klaus