Looks like Garmin charges for some updates and others are free. I took a quick look at their site and found some map updates going for upwards of $80 and some were free. Those seemed to be for newer cars that had a Garmin system installed when the vehicle was purchased. In those cases, it looks like the updates are free for a few years, then I assume they are paid.
For example, here's a map for North America on the Garmin site, called the "City Navigator," it's $99.
https://www.garmin.com/en-US/c/road-maps/?FILTER_REGION_NORTHAMERICA=true