Hehe! Maybe you should just blow the money on somewhere to live, first! Actually owning a building means you have far more rights, too!
The card will be free, or a few dollars. Loading it will not count as the purchase. In any respect, there's no way you'll be able to load a billion dollars on a pre-paid card.
I'd have a ridiculously large old Castle style place built to live in but make it more modern on the inside. With insulation if needed, electricity, and it wouldn't be complete without a moat full of gators and a draw bridge. Adding the gators in the mix might not make it one thing but I think of it as one needing the other.