I know there was a caboose in Leadville that was for sale for some time, but when I was up there recently it was gone. I bet if you called the CRRM in Golden, they would probably know what is available around the state. This site has cars for sale, some at very reasonable prices, but you would probably pay more for the transportation than the cars themselves.
[www.railroadtrader.com]
This site has a caboose for sale for just $10,500, but I bet shipping is extra.
[trainsale.com]
Ken in Buena Vista