I recently came across an American book for people who collect old military vehicles, as in tanks. The 1994 book gave details about how to refurbish and maintain your tank. It turned out that about the cheapest tanks to buy at the time were British Centurions and Chieftains. Both were being sold off in some numbers by the Ministry of Defence around 1994 for $10,000 a piece. But the book advised going for the older Centurions, originally designed during the Second World, as the Chieftains were a little more complex and difficult for the enthusiast to maintain. I seem to remember when I was younger a lot of ex-Polish Army T-34s were being imported into the UK by collectors. I believe the customs forms described them as "agricultural vehicles", as in heavy duty tractors.