There are no fees for using GPS signals, and most GPS models are sold without requiring any ongoing costs. However, there are optional costs you're likely to incur with some GPS models.
The maps in most navigation systems can be updated to show new roads and points of interest. You might want to purchase updated maps every few years. Update costs vary by manufacturer, but you can generally expect to pay $50 - $200.
Traffic Data Service
Some GPS models can use real-time traffic data to help you avoid problem areas. A subscription for traffic data service can cost $50 - $120 per year.