Sometimesright is right.......at least sometimes.
http://en.wikipedia.org/wiki/USS_Iwo_Jima_(LPH-2)
The average Joe may be able to afford the initial cost of the purchase, but by the time you move it from where it's stored to where you are going to keep it and get a berth for it somewhere else, you'll be WAY over your initial price. After you get it to your temporary berth, assuming you want to sink it as a reef, you'll need to do millions of dollars worth of work to prepare it for sinking.
The cheapest part of the entire operation is the scrap price, which is actually just enough to pay for the Navy's paperwork to release the vessel and not a reflection of the true price for that much scrap.
Personally, I would LOVE to have my own aircraft carrier, but I'm not a billionaire and won't be anytime soon. Even if all it was used for was a home away from home, it's just not affordable. A few tens of millions spent on a nice yacht with a heliport or two is about all anyone can afford except the largest of navies.
Even then, the initial cost of a new carrier is the cheapest part of ownership. The U.S. Navy spends more each year to operate and maintain a carrier than one costs.