I've actually been looking into refurbishing a newer railcar and kitting it out much more like a home. There's a lot you can do and equipment like older Metra gallery cars along with more recent commuter cars are an excellent starting point.
My cost comment comes from seeing cars "surplus" for a few thousand dollars, but I'm guessing they might need significant upgrades to be eligible to hook up to Amtrak, not to mention being comfortable for the owner.