umm... I haven't looked at one in 9 years. Bought my G-310 for around $300 9 or so years ago. That was my second electric guitar. I would imagine $400-500 now.
Hi, I'm Peter
im looking for a second guitar two so do you think its worth the buy
Depends what kind of music you like, really. My G-310 was good for hard rock, but not much else. In that price range is also the Fender Standard Series Strats and Teles, G&L Legacies, a few Schecters, a few Ibanez models, the PRS SE series...so you have a few options.
Hi, I'm Peter
the g-400 is good, its made closer to the spec of the gibson sg '61 reissues....(dont quote me on this), and includes Gibson designed pickups, where as the G-310 is shaped a bit differently, and uses epiphone pickups. For a second guitar, save up for the G-400, they are a huge leap from the G-310 by far, and the cost difference isnt much.

Gibson Les Paul Studio w/dirtyfingers pickups
Gibson Joan Jett Melody Maker
VOX ac30 head
Marshall 1960 4x12 cab
Fender Hot Rod Deville
Get the tony iommi epiphone G400 SG, it's the only one that sounds anywhere near as close as a gibson SG, and it actually does sound pretty close. It has gibson made tony iommi signature pickups.