Andrew,
In 1972 four friends and I looked at buying a B-25 that was in good condition for $10,000. The only problem was that none of us had the $2,000 each we needed. Would have been nice because it was just after that they started filming "Catch-22" and nearly all of the B-25s in the country were used. They were returned to their owners in very good condition.
(I wonder what the heck we would have been able to do with it if we had gotten it. By 1974 there were three of them just sitting at the old South Omaha Airport [no longer exists], somebody had bought them and then went broke.)
It's funny, warbird prices stayed low until about 1980 or so when they suddenly made that tremendous leap (Mustangs went from about $150,000 to a million in nothing flat) - and then have stayed pretty constant ever since. If you had one in about 1978 and sold it after 1982 you could have made a fortune. Otherwise, they haven't kept going up in value.
Then again, the price of admission is probably the cheap part...
Best regards,
Rick