i cant say that i could recommend anyone who specializes in JUST real estate but i can offer up my thoughts on the subject.
i think PPC is def. the way to go as trying to optimize to be found naturally when it comes to real estate site is often difficult and nearly impossible.
what i have found is that most real estate sites or realtor sites are usually canned solutions supplied by whoever the real estate company that you work for is and it usually lives on their site. most of them consist of a homepage then links to offsite database and or URLS. pretty hard to optimize something that isn't in your control.