The lowest cost way I can think of is to buy a P-51 in flying condition, take a ride in it, and then sell it for more than you paid for it.
I recall an advertisement in Flying magazine in 1969: "P-51D in flying condition for sale. Includes spare Merlin engine. Asking $18,000."
Shucks, I bought my Ercoupe in 1989 and it was $8000 then. Today it'd cost about as much as that P-51D in 1969.
One day 20 years go or so I flew over to Kissimmee airport and visited with friends. I cranked up and taxied down to the end of the runway for takeoff. The TF-51 Crazy Horse was sitting there, doing a run-up. I did a run-up, too. There we were, two natural aluminum airplanes, one made I guess in 1945 and one made in Feb 1946, canopies open, engines ticking over. Pretty cool. I guess that's my "ride in a Mustang."