Can I build a sustainable home for less than buying a ready made house?

Well, there are many factors, but with the huge inflation in the housing market, it is almost impossible to buy a home without indebting yourself to a life long mortgage. If land costs could be resolved, the cost of building a sustainble home is fraction of the cost of buying an existing non-sustainable home.

Buying land and building a house takes a big chunk of money. If you don't have that money ready then you need to find a way of funding the project.

If you need to borrow money, there are many banks and building societies which now support self build projects. They will generally provide finance on a stage basis, and will only provide a percentage of the total build cost. So you will need to have a little bit to get going, at least 5%.