For those looking for low-end servers, I spotted this one on ebuyer http://www.ebuyer.com/product/140194 for £130 inc delivered.
It's a bit older - Intel 7230 Server Chipset (ICH7R) and a 3GHz Pentium D 925 with 1GB ECC DDR2 It does however have a full ATX board so lots of expansion in addition to 4 SATA onboard, and have 3x5.25 bays so you can easily fit an extra 4 drives with a cheap bay convertor in the future.