Apple is "extremely cheap" because "the stock will be at $600 [again] in the next 18 months," Howard Ward, Gamco CIO for Growth Equities, told CNBC on Thursday.

The iPhone maker was the darling of the first nine months of 2012 — soaring 65 percent to an all-time high of about $705 a share. But since September's peak, the stock is down more than 30 percent — half of which was lost since the beginning of this year.