Like you say, double the material, now, i may be wrong, but double 99.99 (or 89.99 at the minute) is certainly not £300, now, even if were talking double the mATX cases, at 129.99, thats still only £169.98 so where is the extra £30.01 coming from? Also, as its an acrylic case, and its just basically pieced together, couldn't you save manufacturing costs by leaving it to the buyer to build it his/herself?
I understand your reasoning however, and the cases you produce are beautiful, and from what everyone says top quality, so guess we shouldn't put you down!
Double an S2.0 (£140) was just a rough approximation, in actual fact there is a LOT more, this is all of the 5mm acrylic which goes into an L1.0 and X1.0 respectively. In addition because the L1.0 panels are much larger they don't tessellate as efficiently into a standard sheet of acrylic.
JR