I denote classes (in South Florida) by household income as follows:
Lower <80k
Middle > 80k but < 225k
Upper > 225k
Lower <80k
Middle > 80k but < 225k
Upper > 225k
That's just my personal definition of lower income seeing as how places even in bad parts of downtown are about 800-1000 per month for 2 bedroom. Add 300 more for 1 more bedroom.