There should be a sticky for this kind of questions.

1- Don't even think about solo mining. It's not worth it unless of have lots of GPUs.

2- NVIDIA is bad for mining. If you do get the 460 and if you mine 24/7, you will make 1 bitcoin per month (more or less). Check the calculator at http://www.alloscomp.com/bitcoin/calculator.php.

3- It is highly unlikely that it will cover the electricity costs, but that depends on where you live and on how much do you pay for electricity.

At current prices, 1 bitcoin is around $7. Prices can go up or down...