Let me put it to you this way
At the end of 2013, a Radeon R9 280X made about $10/day in Nov-Dec 2013. $7.50/day in Jan 2014. $5/day in Feb 2014. $2.5/day in March 2014, $1.50 in April 2014, in the summer of 2014, it made ~$1/day, at the end of 2014, it made $0.25/day.
Why? Because you are not the only one "thinking" of this idea and got money to throw around. You got competition.
Where exactly are you getting these numbers from? An R9 280x mining Ethereum TODAY on $0.10/kwh power makes $2 per day.
2013-2014