While bicycles are included in the definition of 'vehicle' the drink driving section of the Land Transport Act refers to 'motor vehicle'. This is quite a significant difference. For a bicycle to be classed as a 'motor vehicle' it must be 'mechanically' powered.

While there may be an argument that turning pedals is a form of mechanical power it is not cut and dried. (However, cops can still confiscate your bike if you're operating it dangerously and good luck crying to a judge that your drunken cycling was perfectly safe :)

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You could go to jail for up to 3 months but generally it will depend on your previous driving record, if you have a pretty good record you will probably get a fine and your licence disqualified. Possibly worth talking to a lawyer represent you on this.
http://www.youthlaw.co.nz/page/Road+Rules this link outlines some penalties, scroll to the bottom of the page.

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