In addition to the amount payable to your lawyer (based on your own contribution or the hourly rate), additional expenses may be charged, particularly in the event that your case goes to court. Examples of such expenses are court fees and costs for issuing a summons. Your lawyer can give you more information about these. You can also learn more about procedural costs at https://www.rechtspraak.nl/English.
Finally, as well as your lawyer’s fees, administrative costs may be charged, for example for sending registered documents. Your lawyer will inform you about these as well.