Rummaging round in Hobbyking, I came across the Orange Pi. It's like a Raspberry Pi, but cheaper and with more.
£6.31 gets you an Orange Pi, with a quad core, 1gb memory, 10/100 ethernet, card slot, wifi and 4 USB ports
£14.04 gets you an Orange Pi Plus, with a quad core, 1gb memory plus 8GB flash, sata and gigabit ethernet and 5 USB ports.
The Raspberry Pi 3 is £30, by comparison.