For inert gas exit bag, I've heard nitrogen cylinders are difficult to get delivered to residential addresses in the U.S., but some posters have been able to get argon delivered, which can be used instead of nitrogen. Don't know how difficult it is to get nitrogen cylinders collected.
Inert gas cylinders cost roughly $100-$200 dollars, depending on size. Some people connect the cylinder directly to an exit bag, but it's advised to purchase a gas regulator, which costs roughly $100-$150. Then you just need to buy oxygen tubing, and the plastic bag.
Don't know much about CO. As well as the charcoal to burn, people advise to definitely buy a CO detecter to ensure you have a high enough CO concentration to ensure a peaceful exit.