So the schematic, PCB, and case has been designed, and here are the costs:

1. Components - £12.835 from RS & Farnell 

2. PCB - £0.730 including shipping for a single board (£7.3 for 10)

3. Case - £5.96 for both halves printed in ABS, with 0.2mm layer height.

The PCB has been ordered, and the case is being printed, components will probably be bought once the PCBs arrive, as they only take a day.