$130 today for no updates once iOS 8 hits, or $250 for udpates easily into iOS10 (assuming Apple follows their own footsteps).
If Apple follows their footsteps, iPhone 5 will only go to iOS 9. Every iPhone has had 3 iOS updates since the 3GS. Since the iPhone 5 shipped with iOS 6, it will be upgradable to iOS 7, 8, and 9.