They are ussually around $200-$400 (Depending on which kind you would like, 3GB,8GB e.c.t) Also the monthly cost, again depending on the plan you get.
between $200 or $400PHONE QUESTION
If you are looking for brand new iPhone, The cost depends upon the model and network to which it has been locked to. Basically it would cost around $200 to $500. You cannot get iPhone without a service.
If you need an used iPhone, You can get best deals from Ebay.Com Unlocked iPhone models would be costlier than network locked iPhone models. If you want the price to be lowest, You can get a network locked iPhone and unlock it yourself at low cost. You can unlock an iPhone safer and easier using remote unlocking service. You can get the remote unlocking service for an iPhone from http://www.wickedunlock.com/apple/rs16wp8/ at affordable cost with easy unlocking guide.