Even spending $300 on a F2P MMO is seldom enough to make you "1337." So many of the "must-have" items are consumables. Throw in some money for a skill reset or some other items, and you can easily rack up a tab of a few hundred dollars just to stay afloat.
If you truly are dedicated to an MMO, then a P2P is a much better choice. Because no matter how much you are willing to spend, you'll only have to spend $15 a month. Whereas with a F2P...well, there are stories of top players who have spent thousands of dollars on a game.