Hawk Wargames have responded under point 2 here, but it boils down to the use of expensive resin for quality reasons, and then this hideous paragraph.
"Secondly, the nature of the system and its adaptable design has a large impact on cost. Unlike most other resin scenery lines, ours can be modified, added to and used in thousands of combinations, offering near limitless potential to keen modellers. We always strive to innovate and to go the extra mile with new releases. Pushing boundaries into new realms makes direct comparisons with existing products difficult of course, but we feel that we are offering so much more than simple, inflexible scenery blocks."I'm not sure how this justifies higher costs, because we either paying for the privilege of modular terrain (I have a hacksaw, it's all pretty damned modular to be) and/or paying for the design work needed on modular buildings, which in all honesty, isn't really "pushing boundaries."
To give an example of the prices, the cheapest complete building kit (all at 10mm scale) is the Residential Building 3 (above) and is available for £35 (although you could build something smaller and cheaper from parts I assume).
For £35 you get a building that's 11.8cm wide by 8.4cm deep and 9.9 cm heigh, which is fairly tiny. Made up of a "lobby" section surmounted by walls made up of tiles (See the windows? Each bank of three is one tile. 30 are needed to make the walls above the lobby). The complete parts list can be viewed here.
So one (tiny building) for £35. You're going to want more than that though. The FAQ recommends using 10 buildings on a 4'x4' board. That's £350 for 10 identical buildings. Say you don't want all the same building though. Well you can buy a City Pack of ten different buildings for £460. And that hard earned cash will get you this...
Do things get worse? Well, yes, because you probably really want 15 buildings for a well filled board. You could buy these in bulk from the Metropolis pack, for £740.
Anyway, that's worked examples over. Phil on The Shell Case digs into the quality of Hawk Wargames' response, and made points I'd only be repeating here I was to go on. Click here to have a read.