Changing the administrative or technical contact of a domain name is usually free. Just like changing the nameservers.
If you want to change the owner of a domain name you may have to initiate a trade. Depending on the TLD costs may be charged for this operation. These costs are either a set administrative fee or equal to a one year period of the domain name.
Please note that some TLDs may differ from this. As a rule of thumb you can say that if our control panel accepts your change without any warning that no costs will be charged. Most TLDs that charge for such things are a manual operation already and you will be notified of these costs during the process.