Last time I went there (February 28), they had only the generic drink menu that appears at all WDW resort lounges - no specialty drinks specific to the Polynesian were listed, not even in an insert. That doesn't mean you can't ask for them - if the bartenders know how and have the ingredients, they will make them - but it does mean you can't get accurate pricing from a menu (although it's possible some of them might be listed on the restaurant menu at Ohana - you just can't get them from the bar menu)
Last I recall the lapu lapu was about $14 and the backscratcher around $10.