I have this kit:
http://www.nitrousexpress.com/Pages/ImportStage1.htm
Comes with 10lb bottle.
Plus a purge. Asking $400 with a full bottle. (thats over $50 in NOS)
I also have a 6inch section of 2.5inch pipe with the bung welded in that will be included.
I also have an SS fuel feed line for a DSM with a "T" for the NOS. $50 for the SS line and with that, you'll have a complete bolt up ready to go kit for a DSM.
It will be going up on ebay in a few days,.