Seconded. Not sure about New York, but the real estate market over here easily reaches Darth Vader levels in terms of evilness.

Just started this project this morning, but the goal is soon! Once I get a decent product working for NYC it shouldn't be difficult to branch it off into other cities.

Also, every friend I have who tried to rent an apartment in São Paulo either failed or ended up with something wildly overpriced. If you could make this generic enough to use in other countries/cities it'd be great.