Hey Argus, long time no talk. I think the cheapest option by far would be to import the 406 LHD from france or other other LHD country. I think its been discussed that if you were to import the car without the engine and transmission, and maybe just for insurance, take apart the car as much as possible, and ship the car to the states in pieces (easy to put back together pieces) then you should have no importing issues. Also, 90-100% of Extreme's DVD would apply to your build so you wouldn't have many build issues. All you would want to do is source a strong FWD engine and transmission setup that you would install using custom subframes and mounts.
One strong FWD drivetrain choice could be the Dodge SRT-4, comes in Manual 6 speed and is a turbo motor and can be tuned to 400+hp...should be affordable to service as well...
good luck to you