Cold bluing usually comes out looking kind of cheap and nasty, and usually does not hold up to wear very well. Results vary a lot depending on the steel, and the bluing used, too.
Take a look at the rust bluing process. Most complicated pieces of kit required are a pot big enough to boil the larges part in, and a container large enough to keep the parts in a humid environment for a few hours at a time.
Birchwood Casey Plum Brown has gotten good reports as a rusting agent. Lot's of info on the web.
If you want to go the hot blue route, I suggest doing all the prep work (sanding and cleaning) and find someone set up already to do the bluing. A couple pounds of 650 or do degree melted salts is, to say the least, a safety issue, and there are a few guys around that are already set up.
Cheers
Trev