If you have the engineering capacity, and your business model can at least sustain some amount of overhead, you can build your own CDN. Look into PhoenixNAP an

If you have the engineering capacity, and your business model can at least sustain some amount of overhead, you can build your own CDN. Look into PhoenixNAP and other similar providers that are located at non-profit peering sites and have reduced bandwidth costs. PhoenixNAP (as the example) will lease you a mid range bare metal server with 16GB/RAM and 100TB of data/mo in the $150.00/mo - $300.00/mo range (depending on your processor needs; well optimized nginx doing just proxying should scream). You can't exceed some unwritten bandwidth cap because you're explicitly paying extra for the 100TB of BW. For 20 caching servers firing 2PB/mo you're looking at around $3000 - $6000/mo... Seems like you could optimize this down with fewer high powered caching servers and paying for the extra bandwidth... is the engineering time and $2500/mo really out of reach? Best of luck.