Affluence could encompass several parameters:
Wealth (property ownership);
Access to services such as education and health;
Access to clean natural resources;
Low levels of criminality.
Property prices in each locality might be easy to obtain from real estate agent sources
Ratings for schools or medical facilities in each area might be published
Generally, where public statistics are collected on a locality, they will be related in one way or another to affluence. A useful strategy might be to collect as many of these diverse data sets as possible, and to learn a composite affluence score from the data. It is very likely that all of these parameters will be correlated to a greater or lesser degree, and so you could accurately learn about affluence from a small number of these parameters.