A new study points out what some San Luis Obispo County residents already know. SLO County is one of the least affordable areas to live in the U.S… According to the Tribune, a study done by Porch shows the cost of living in San Luis Obispo County is 9.5 percent higher than the national average, just below Napa. The cost of housing was a major factor in the study, with San Luis Obispo County coming in at more than 51 percent above the national average.