Oh, I so wish we had DTFB in Brizvegas....but alas, it is a suffering we must endure

.
Anyway, to answer your question: I have bought foamboard from the Riot art store at the Chermside westfield. I think it is a bit heavier than DTFB, but as I have never seen DTFB I can't truly say. Last time I bought some, it cost me $11 for an A1 size sheet. They do have different colours, which might be handy.
A few guys at my club buy depron (usually from the 2 local hobby shops). But that is expensive also.
Hope that helps.