I mentioned it in an earlier post:
In the end we decided that mass walls were not required and that the slab was adequate.
We had it modelled with AccuRate and it didn't seem to make a difference to performance (if you can trust the operator and software).
It wasn't required either according to the glazing mass ratios quoted in Paolino and Baverstock's manual.
http://forums.envirotalk.com.au/Thermal ... t8093.html
Information given to was that Formatech cost about $160/m2. for a 150mm wall.