Good sources on what? Server pricings?

We charge for an Dual Hexcore Opteron, 16Gb ECC, 4x2Tb with 1Gbps burstable connection just 99€ a month. Tho the bandwidth is calced among max 150mbps average upload traffic. Downstream doesn't matter to us, and this would be mostly downstream most likely. Tho that is extremely cheap for a dual cpu node, and we are likely to increase that pricing at fall.
For storage servers we charge for an E350, 8G, 4x3Tb, 100Mbps Unmetered, 89.98€/Mo + 125€ setup fee.
Both of these two are very cost effective options, the latter coming to just under 7.5€/TiB/Mo.

Zfec: Good, a common, well used library. Eliminates chances of making mistakes, and puts the pressure of bug fixes on 3rd party on the erasure coding front.

Free data sources? What's that?
Please explain why transit capacity becomes storage available?
Does the system constantly transmit the data again and again and again even tho no one is requesting it?

If the system is built so that bandwidth == storage maximum, it becomes INSANELY expensive.
Most operators still pay something like 1.5€+ per Mbps, that's 1500€ for 1Gbps connection -> ~300Tb a month transfer capacity. That's 5€ per Tb! For a large operator like that the cost per Tb of storage to offer then quickly quadruples!
Nevermind a gazillion of other issues.

In any case, as long as the bandwidth usage is sane, for example i have a warehouse which is limited to 20/1M connection or über expensive SDSL, but it needs to be heated up during winters, 5-6 months of a year we need to spend money on heating it up, whether it's oil, bitcoin miners or to this. If BW usage is low, it would make us much sense to put in a couple kWs worth of disk arrays there over time as the capacity gets filled.

Which reminds of compression? On the plans?
Also, do you intend to build in algos separating colder data from warmer to emphasis warmer data to those storage nodes with more BW and colder to the ones with less BW, or do you intend to let natural selection do the job for you with some ultra simple idea?

If the price per TiB on end user ends up cheap enough i envision a lot of parties will use this for backup purposes.