The key isn't chipped so its just a standard key; but it opened the doors and started the vehicle. I need a replacement. Where should I go, and how much should it cost?

Sidenote:
I bought the car two days ago. The title isn't transferred and I don't have insurance yet, but I was told by a locksmith that if I talked to the owner and got a picture of his ID from him he could make the key... For $150. But that doesn't sound right considering it is a STANDARD KEY. The current owner/person who is registered on the car is willing to cooperate with what I need.

Its Sunday and I can't talk to the DMV or a dealership or a hardware store. Just looking for information before then.