Given the tremendous increase in Apple’s (AAPL: 476.68 +1.67%) stock price, many analysts are nowwondering if Apple stock has become expensive. However, others claim that AAPL shares are cheap based on the furious earnings growth experienced by the company.

Yesterday, Deutsche Bank (DB: 46.26 +3.17%) increased their earnings estimates and price target for Apple. Just a few months ago, they expected Apple $13 a share. Now with the release of iPhone 4 and the iPad, Apple is expected to earn $18 per share.

These earnings increases has resulted in Apple becoming an “accidently cheap stock” according to Mad Money host Jim Cramer. He believes that Wall Street analysts have consistently underestimated Apple. Piper Jaffray (PJC: 24.12 +1.26%) had originally estimated that Apple would only sell 900,000 iPads by June. S.C. Bernstein had estimated much higher, but still only predicted 2M iPad sales. Of course Apple just announced that they have already sold 3M iPads.

Cramer likes that fact that analysts are increasing their estimates for Apple, but thinks Deutsche Bank’s estimates may still be too low. Cramer predicts that the tech giant could earn $19 per share. That would mean that Apple only trades at a multiple of 14x earnings and could result in significant upside in the share price.