How is it possible that amazon charge $0.050 per GB (for more than 350 TB / month ) while DigitalOcean charge $0.02 per GB for each extra GB and 0.005$ / GB for the 5$ plan?
How can they make any profit?
Given you can get 1Gbps from Cogent for ~1K/mo (at least that's the price I heard last time they were having a sale) that works out to $0.003/GB, so both are making a massive amount of profit.
Contact your local cogent rep. If your dedicated server is in a building with a cogent feed you can probably get a line to it. I'm not sure their current non sales pricing and that might require a 10Gbps commit.
