Depends on how many you want, what you need them to do, and where you want to put them. There is no quick and dirty answer, particularly not one you're likely to get from a message board on the internet. But, I did a little search, and came up with this page:
http://www.kiomag.com/quotation_QUOTE
Deploying kiosk technology is not a simple task. Significant
objectives are involved. You want to serve your customers
faster, better. You want a return on your investment. We
understand this. KIOSK Magazine offers you Kiosk
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for your kiosk project. Whether it is a single keyboard, two touch
screens, or installation service for three hundred kiosks . . .
we can handle that! We will submit your request to leading
companies for real-time product information and quotation.
No project is too small, or too big.