Hi Jeff;
What style RMH were you hoping to build? A "J tube" ?
If so you can do this yourself with a bit of guidance from the rocket scientists here at Permies.
If your wanting to build a batchbox then there is some metal fabrication needed, OR you could buy those pieces premade from
dragon technology...
An old school RMH was a "J tube" 6" or 8" and it used stove pipe to heat your rock and
cob mass.
A modern day J tube can use pipes thru a mass or it can use a brick bell as a mass.
If your worried about making cob, Don't be, it is simple simple and if you build with bricks you will not use much cob at all.
Let us know more about your wishes and plans and we will try to guide you to your first successful RMH build.
One thing to remember is when you build with cob everything can be disassembled and redone quickly and simply.