Not sure what you're having trouble finding. Pricing is easily available on the internet for many CDN providers (basically all except LimeLight and Level3). Some examples:
- Rackspace Cloud files (using Akamai's huge CDN) is US$0.18/GB
- MaxCDN (the pay-as-you-go version of NetDNA) starts at US$0.10/GB
- Voxel VoxCAST starts at US$0.10/GB
- CacheFly starts at US$0.39/GB
- GoGrid (which uses EdgeCast) starts at $0.25/GB
You get volume discounts, and depending on provider can better pricing if you are willing to commit to certain spending under a contract-based service.
Obviously there is more to it than just price. Stability is paramount. Many of these CDNs are architected quite differently, have different features, and offer different performance levels for different regions and use cases. For example, the anycast-based CDNs (such as CacheFly and MaxCDN) typically offer the lowest latency, and are great if your customers are in secure environments that must white-list external providers by IP address. But those same providers also seem to have fewer network nodes and peering points than CDNs that use DNS-based redirection.
See CloudHarmony for a more complete list of CDN providers.