Macchiatobin is a pretty good alternative these days. Mini-ITX form factor, 4 relatively high-performance cores, good amount of RAM and PCIe/SATA/10GbE.
The MACCHIATObin line does charge over 300€ for a underpowered 4-core processor with 4GB of RAM, and 500€ for a 16GB model. That's the price of a low/mid-range COTS x86-64 box.