FlyerTalk Evangelist
Join Date: Dec 2002
Location: Danville, CA, USA;
Programs: UA 1MM, WN CP, Marriott LT Plat, Hilton Gold, IC Plat
Posts: 15,722
You might as well ask, "How much is an apple?" Prices vary from country to country.
However, I can tell you that I bought a SIM card in Italy recently for 15 Euro, but they were offered in many denominations. And unlike Telestial, when you buy a SIM card in europe you will get most of your money back in call time. So if you buy a 15 euro card, you'll get 10 euro credit. And I think you do even better on refills.
If the phone is just for emergency, then maybe you just want to activate international roaming (assuming it is GSM and has euro bandwith) as you will then pay nothing if you don't use it. But you would be surprised how handy it can be, especially when you get lost, or need to meet someone, etc. For that reason I would highly recommend buying the SIM card when you arrive. The per minute charge varies but is usually .15-.50 euro per outgoing minute, and unlike the US, all incoming minutes are FREE.