Till about 2 or 3 years back, the usage of the Google Maps API was completely free for developers and others who embedded the service in their websites or products. However, probably due to the excessive load brought in by some users/companies, Google decided to charge an additional fee for usage beyond its proposed free usage limit (which is 25,000 map loads per day). For every 1000 views after the free usage limit, Google had been charging US$4. Though only a small number of websites that used the service exceeded the free limit (0.35% as reported by TechCrunch), the fee dampened what was otherwise digital geographic supremacy; as some companies, such as Foursquare, switched away from Google Maps after new fee was initiated.
To win back the defectors, and to quiet down public outcry, Google has now decreased how much it charges for use of Google Maps API: $0.5 per 1000 map loads after the free limit ($1 per 1000 views for JS Maps API v2). Another change is Google doesn’t automatically enforce the fee upon everyone. Google gives consideration to the temporary spikes that some websites face. Google contacts the developer only after the free limit has been exceeded by the website or company for 90 continuous days. Speaking as a common Internet user, this looks quite fair.
Aside from the mentioned above, Google has also upped the free usage limit for styled Maps API to 25,000 (it used to be 2,500); thus eliminating the difference between styled Maps API and unstyled Maps API (styled Maps users can customize the API to their needs).
You can find more about the Google Maps API by paying a visit to the FAQ section of the Google Maps API.