I think you have your terms confused. if your going to buy a phone better know what you are getting.
Jaikbreak allows you to use unofficial and unsupported apps and themas and use unauthorized app store like cydia.
unlock allows you to use a cell phone on any gsm network like AT&T phone running on t-mobile.
any phones sold early on will go for big dollars I promise you. 3GS was going for $1000 plus on release. jailbreak unlock will mot be out till after iPhone 4 release. nobody knows exactly when but word is not long. and jailbreaking and unlocking is so easy even a cave man can do it.