We had our prefab delivered a few weeks ago. It was MUCH cheaper than a brick house on site, was well under $1000 a square metre. They build them in 6 weeks but it takes 9-10 months to get council approval, finance, pick your colours etc. And then there were all the headaches of arranging tradies to finish the place off (although the builder can arrange that it costs more than doing it yourself), so almost the opposite to what fionas said

We got a prefab with a LOT of extras (higher ceilings, fancy kitchen benches, fancy cornices yada yada) which added about $20k to the list price of the house so we could have got it for about $90k in the end. This is a 4 bedroom 2 bathroom 2 living area house.