How do you estimate rental prices/vacancy rates for "rich" areas?

[Tom Smith]

How do you estimate rental prices/vacancy rates for "rich" areas?

I see some Facebook posts for roommates for wealthier areas of Houston, TX like neighborhoods of Kirby and Montrose, but how do I calculate what I can actually get for a given property? What resource would be the best to get this information? Of course I want the cheapest and most accurate resource to obtain this information. 

I also may be house hacking a property in these areas, so how do I know how feasible it would be to rent out 2-3 rooms in a SFH and how much people would be willing to pay and how long they are willing to stay?