From Sen and DeLeire (2018):
…premiums of Marketplace plans are 11% lower in Medicaid expansion states, controlling for demographic and health characteristics as well as measures of health care access. These results are consistent with evidence on the composition of the private insurance risk pool in expansion versus nonexpansion states and associated differences in expected health spending.
Medicaid expansion may make private health insurance more affordable for non-Medicaid eligible middle class individuals, but those same individuals may be paying higher taxes to finance the Medicaid expansion. It would be interesting to predict the net effect of Medicaid expansion on middle class take-home pay after insurance premiums and taxes and how that varies across states. Free study idea for anyone interested.