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...
I don't think it'd cover costs, but what I mean is for what I'd be making in bitcoins. I'm unsure of if it's worth the extra costs, and if so, roughly how much the costs would be. ( I live in Australia) Where pricing is f'ing ridiculous lol.