iPhones are locked to individual networks by locking the IMEI number of the phone. This is done in Apple's databases and can be unlocked (whitelisted) only by Apple. This unlock is thus official and warranty still persists even after the unlock itself. After the whitelist of you IMEI you just connect the iPhone to iTunes and sync this information to it. The proper steps are show after clicking on the link in the bottom: iPhone Unlock Procedure.
All the prices depends on the carrier that locked the phone (the one that the iPhone was purchased from). In case the carrier is not listed in our store, please contact us for a price. Contact us via e-mailem or Facebook.
Please check this video that will help you change currency. If you want to order in Euros, you need to change the currency first, and then order. Same for the rest currencies.