How much will it cost to build my own community?

That will depend entirely on what you wish to create, how much you and your group will manage the process yourself, where you are located and many other variables… If you are in the tropics and intend to build yourself, resources requirement will be around $300-$600/m2 or equivalent.  If you are in Europe or the USA this figure could easily double.  This does not include costs associated with infrastructure, which will be entirely site specific.