I will not lie you, there are free and opensource scripts that are the same as your needs, and i have experience with some of them.
Ossclass it's one of them. Some bussiness works great with him, like offerum, a spanish start-up.
I can make a theme that will be like Trulia, Zillow or any other real state webpage.
The platform can be developed from scratch, but it'll get bugs, too many time for developing, and it's expensive.
Regards, Jorge.