Why do some unlock codes cost more than others ?
The cost of unlocking a handset varies upon availability of the SIM unlock code. Some networks will release unlock codes based upon age of the phone or requirements of the subscriber.
Typically in the these cases the price per unlocking is relatively low compared to other options. In the other instances the network will not release the unlock code because of strict eligibility requirements or exclusive sales arrangement with the manufacturer or plenty of other reasons, then the unlock code must be obtained through the manufacturer of the phone.
Obtaining codes via the manufacturer will in most cases be more expensive than through the network. Additionally all networks don't have the same eligibility requirements and some never releases unlock codes under any circumstances. When this is the case, all models no matter the age of the handset should be requested through the manufacturer.