Buy yourself a radeon hd 5870 card for about $200. With 350mhash/s you'll get 1.3 BTC/24 hours. That's 39 BTC/month. It's about $273 with current rate of 7 USD/BTC. Not counting electricity bills. Most likely the BTC exchange rate will go up after difficulty increase, so you'll get even more than $73 profit in return.
THIS is the kind of MISINFORMATION people need to stop spreading so people like stop asking obvious questions like this.
The price of BTC exchange does not depend on the difficulty. Just because it has for the past month and there seems to be correlation between the two doesn't make it so.
It's infact the opposite. The price is based on supply and demand not difficulty. Right now the demand is up because of the hype and spreading of bitcoin misinformation such as above post are attacting people thinking they will make easy money. This is again obviously not so.