You could pick up a single-slice Acorn RiscPC with Ethernet from Ebay for around 150 GBP, install 2 HDDs (there are three internal spaces so you can choose between CD or floppy) and install ArmLinux. The PSU is huge but only 70W.

Make sure you get one with Ethernet as the Ethernet module was not a standard item and are now hard to source (and for £50-£100, rather expensive).