Yeah the cable is expensive but worth it. Then rocksmith is basically guitar hero but it has you playing along to the actual notes. It also comes with lessons and has an insane amount of user submitted songs.
http://www.amazon.com/Ubisoft-Rocksmith-Not-Machine-Specific-630570063043006306200/dp/B005OSFUZI
Probably your best bet.
Cord is usually included in console versions of the game, but if you get it on Steam you'll have to buy one seperately. Here it is on Amazon
That seems like kind of a rip-off, but the PC version also includes the Bass expansion, which is normally 20 bucks, so I guess it sort of evens out.