FD - a tried-and-true, almost-free keyboard-protection method, widely used in bars and taverns (a bartender's hands frequently are wet, often with stuff that will turn sticky, and cleanin, repairin', or replacin' a cash station's keyboard is a much bigger deal than is the case with a 'puter keyboard), is simply to cover the keyboard with clear kitchen wrap. There are commercially available keyboard protectors, too, tailored to fit specific keyboards.
Another option is the
Virtually Indestructable Keyboard. There are several models, rangin' from basic 85 key (great for handhelds - beats helloutta thumb-typin') to fairly full-featured 109 key, all in standard layout. One version even lights up, and all are silent in operation. A little shoppin' around will turn up any of them for well under $50 - as little as under $20 for the most basic model.
I've used 'em, and they really take very little gettin' used to.
