Google has a lot of settlement free peering, so the bandwidth itself is going to be close to free, although the infrastructure to support it would not be. They

Google has a lot of settlement free peering, so the bandwidth itself is going to be close to free, although the infrastructure to support it would not be. They also don't have to worry about being present in as many peering locations as most networks of comparable capacity, as their services aren't that latency sensitive, which also helps reduce their infrastructure costs.