Im sure stainless would be the best piping to use but i can get 2 1/4" tubes in 10' lengths for $20 or 2 1/2" @10' for $25 or 3" @10' for @30 "aluminized" exhaust tubing. Not sure what gage it is till i go look but im working my way toward my true duals. Is that a good price or worth using

 

I'd wait until you can save the money and do it the right/best way. That is with SS piping.