The hard cost for startup right now is either the highest end AMD cards or some specialized FPGA cards that don't mine as fast but use less power. Right around the corner are custom built chips for bitcoins. As far as I know 300 ASIC units have shipped from a chinese company with an unknown timeline of when the next limited run will hit. Butterfly labs, a US company, was to have their product by end of 2012 and still hasn't shipped. (Maybe by May, maybe not). So when the graphics cards are no longer worthwhile to use is anyone's guess. Personally I feel around May or June.
Your profit as a miner is based on the total amount of computational power. Right now the total bitcoin network is around the 60 trillion calculations a second. A single card will do upwards of 1000 Million calculations. Once the ASIC chips hit in volume the total network power will double or triple very fast and keep on climbing.
With all that said here is a calculator to help figure things out.
http://blockchained.com/profit/index.php
If you put in 1300 you'd need roughly 100 days to break even as is. That assumes the value says the same and difficulty stays the same. Difficulty has historically always climbed.
Now if electricity is free that reduces the cost drastically as a GPU is a power hungry device. If you already own a high end gaming machine then there's no reason not to put it to work.
