David Blasco's website lists several Craigslist machines, as well as having interesting & informative articles. Craigslist is a good resource to search. Right now running Pre-Unit (IB, CI) Bullets seem to be found in the $2500 - $4000 range. Most US bullets are from 1970's to 2008, when they were superseded by the new UCE (Unit Construction) machines. If you plan on some distance rides and want to spend more time riding than wrenching the UCE is perhaps a better choice. It already has a steel rod, needle con rod bearing and better piston, as well as hydraulic valves, 5-speed transmission, front disc brake and fuel injection, all for about the same money.
https://www.royalenfields.com/What's your experience level? What are you hoping to do with an Iron Barrel Bullet? They are basically a 1940's design that were manufactured in India for nearly fifty years.
Once sorted out they are reasonably reliable, ridden within their parameters. Pushrods, carburettors & points are pretty user friendly. They run reliably on flat ground about 50-55ish, so are better suited for back road excursions. Unless you pump in about $2500 - $3500 for a better bottom end with steel con rod, forged piston & alloy barrel it'll just grenade if you abuse it. A stock machine requires a "mechanically sympathetic" owner handy with tools, or you'd best be closely related to Jay Leno. Parts, tools and manuals are readily available from Hitchcocks Royal Enfield (
https://accessories.hitchcocksmotorcycles.com/) in Solihul, England. Royal Post / Fedex is 4 - 10 days out and they give excellent, knowledgeable service.
Let us know more about what you're after and our motley crew here will be happy to help. - ACR -