Finished with story mode? Didn't rack up nearly enough cash to spend 200 million across 3 characters? Contemplating restarting the game to take advantage of Lester's assassin missions just to make enough dough? I have found there is no need! (Unless you really want to own the golf course, that is)
Anyways, to get the achievement the easy way all you have to do is go into the stock market. Pick any stock you want and dump all your money into it. Immediately sell the stock and get all your money back. Rinse and repeat. Every time you put money in a stock it will count it as money spent. Do it until you've spent 200 million and the achievement/trophy is yours!