I work for a company that restores heritage buildings, and have not done many jobs on my own, so it's hard to put prices on things!
The Letterbox was a side project at home over 2012 and it took about 6 weeks full time all up, working a bit here and a bit there. The materials cost less than $2000AU.
If someone was to point at my letterbox and say "I want one, how much?" I would probably ask for 20K, which would be paying me 50% more than what i am earning at work,
because the work is more skilled.
But i have heard that Australia, and Melbourne in particular pays really well for plastering? Thats what my friends from the UK say.