What's the point of owning an iPhone without a plan? Do you realize even if you unlock it you still have to subscribe to Rogers or Fido?
If you do not intend to use iPhone to the fullest, you should probably consider getting an iPod touch. It's pretty much the same except no GPS/Phone functions/3G network accessibility.
AT&T was going to sell it for over $600 if I remembered correctly (without a contract). So expect to pay more than $700 for an unlocked one.