In singles from a distributor you probably have to shell out a little bit more than $15 - http://www.digikey.com/product-search/e ... =AD9223ARZ
is $20. Shipping costs depends on where you're located - I guess that your're not living in the US?
12 bits isn't that much so it will survive a bit of noise at the power rails without losing too much of precision. But still, you will have a system with mixed digital and (rather) high frequency analog signals so proper electronics design is mandatory to keep the digital stuff from destroying your analogue signals - especially if they are low level.
Unless you're sufficiently experienced I strongly suggest that you open a new project thread and tell us what you're going to build and with what parts and see if the DP community can help you out with the design and hints for getting it to work properly in real life and not only on paper.
Ian.... It would be fun to see a world heatmap based on the country of the last ip address each user had for his(hers) last login.