and yet, some do...with a fair degree of success, so it is not exactly an insane idea:
Speedwell of Hong Kong Â» Speedwell´s Junk Rig
just be sure to get someone to design it for you.
As for cost, at the JRA site I saw a complete Junk Rig
including the mast
for a smaller boat
advertised for $1000 obo. I say go for it.
--signed, the man with no experience whatsoever