Nano-SIM cards are available from:

Cellcom - cost, NIS 99
Orange (Partner Communications) - cost, NIS 88

Will soon be available from Golan Telecom, though price has yet to be announced.

Unannounced if/when support will be available: Pelephone and HOT Mobile as well as MVNOs, such as Rami Levi, YouPhone, Home Celluar, and Alon Cellular.

The iPhone 5 won't be available for purchase until December, but you can bring it in from abroad. Cellcom and Orange already have Nano-SIMs available.