This site lists all surviving steam locomotives in the USA, Canada, Mexico, Cuba, Central America, The United Kingdom, Ireland, Australia, and New Zealand. I currently know of around 20 steam locomotives in the USA that are for sale.
I don't know how much the owners are asking. I don't always have the owners contact details. I simply note that a locomotive is for sale when I hear that it is. I do list what I know about them but you may need to do a little research on your own.