You are starting at the right place and asking the right crowd. You need to provide more details, what does no budget mean? What resources do you have at disposal to execute a marketing plan even when the budget is limited. What you did by posting here is comment marketing but even for this you need manpower. In the uk for property, there is zoopla and rightmove who have the large chunk of the market. Are you going after the estate agents or home owners? If I had to give you my take on marketing, 60% is your product, if it is easy to use and solves a headache for your target market, it should keep people coming back. This repeat traffic will have no choice but to share it with their contacts but you must make sharing easy. If you want viral help: Your internet marketing plan for viral growth must provide clear understanding of what your product is going to do for your users and it must deliver on this. If you can take away only one thing from this, remember: from the start, only push One Main Message to achieve viral growth. This should not necessarily be your unique selling point but rather your Unique Spreading Point.