As always with nice designs like this, the main cost would be in the manufacturing, which is why mountain mods cases are so butt ugly - their designs are easy to manufacture - angle aluminium frame with flat panels bolted on.

When you start including bends and slots for panels to fit onto (lian li, silvertsone) you require very specialised equipment capable of high accuracy.

Nice design, but i doubt it could be produced for under £500. Aluminium alone would cost somewhere in the region of £100-£150 then coating (anodizing or powder coating) would be an additional £40-£150 and the cost of machining would be range greatly from £50 to £300+ per/hr depending on machine required (from a simple Mill to a CnC laser cutter/cnc press ect.)