3-4 hundred bucks at the dealer. ebay has them, you have to be careful about what may work and what won't. do a lot of searching here first. also thread by member 'ovni'. a good locksmith may be able to work some magic, but don't pay anything until you have a working fob in your hands. all the best!
The 2012 Prius C smart key ($250 at dealer, $175 wholesale) does not include the insert key. If I understand correctly you can get a laser cut key for about $100. I think you can by a key slug insert for about $14. Programming runs about an hour labor. Again, there are those who say they can reprogram a used remote; make sure you get that in writing in case something goes south. The smart money is get it all done at one place-unfortunately, that's probably going to be the dealer so it could be $450 (remote, lazer key, programming)-what a rip-off, eh??
Read my thread on page 3 of this forum "A tip that could save you $150 - $200." Make sure you continue reading the thread thru page 2. Page 2 of this thread has a few important updates!