he easiest and cheapest way is by winning a lottery. The problem with that is that actually winning is close to impossible but if you do win an a ticket for a few bucks you'll be set for life.
Otherwise you just need to work for it.
That is the quickies way to get rich but it is the hardest way to do, you need to be extremely luck in order to win the lottery and considering the total population of the world, you chances are pretty low.