How to carry Xtracycle by car? What is the best way to mount an Xtracycle to the roof of your car?

Xtracycle has a few suggestions particilary a Thule or RockyMounts Tandem rack.

We have a Mazda CX-9 with factory cross bars.  The problem with Xtracycle's suggestion is it will cost around $800 to buy all that gear.  We are looking for a cheaper option.

We were considering the Sea Sucker Talon.   That looks like it might work.  It will be a task to get the big bike on to the roof of the car but we will only be doing this occasionally.  

Our bike is a converted Bianchi which looks similar to this one.  It's around 50+lbs.
If the length of the bike is makes it legal, hitch rack with the bike sticking out would be the cheapest and easiest - You would be no wider than trailers and trucks, but care would be need to remember that. Get a rack fabricated that holds the bike vertically off the hitch, Strop the top roof the rack back to the roof bars. For ideas have a look at here and talk to an engineering shop.

Have a look for ideas to carry tandems - Here is one idea that would work.