Thank you for your reply. An old Intel Xeon E3-1245 is enough with 8 to 16 GB of RAM.
So, what I'm looking for:
Location USA (best somewhere in the middle, because my customer base is spread over the whole USA and therefore I have to have the best possible connectivity to most locations)
Intel Xeon E3-1245
8 to 16 gb RAM
1×8 TB SATA
1 Gbit / s with about 80 to 100 TB (I think 50 TB should do the work as well, but if possible, rather something more)
Budget not more than 150 USD