$0.003/GB is what $1/1Mbps is, at 100% utilization. 324GB is what 1Mbps can do in a month. Perhaps a bit less but low quality providers (HE, Cogent) will do a dollar a Mbps easily. So work backwards. (Another way, you need 3kbps to do 1GB in a month. That times 333 is about 1Mbps, so $1. I'm ignoring 95th percentile billing here.)

Better providers like L3 are around $3/Mbps, last I heard.

So $0.001 a GB means you'd only pay 33 cents per Mbps, which seems pretty low. But maybe at terabit commits, HE goes even lower.. I've only looked at 10G commits.