A bit of a niche product that won't appeal to everyone - Intel's current top of the line i7 NUC.
http://www.intel.com/content/www/us/en/nuc/nuc-kit-nuc5i7ryh…
After shopping high and low (all the Amazons, many US/EU/Asian retailers, all the eBays) and observing price movements, Amazon's $50 price drop today makes it the best price I can find worldwide by a good margin.
AU$690ish from reputable local stores.
BYO hard disk (2.5" SATA 9.5mm max and/or m.2 SSD), RAM (1.25v SODIMM), operating system.
FYI, the CPU in this machine is a dual core i7-5557U with similar (or possibly lower) performance to an i3-4170, which retails for about $170 (to give you an idea of what it's worth).