Medicaid Expansion Incentive Act of 2013 - Amends title XIX (Medicaid) of the Social Security Act to entitle to an increase (bonus) in payments under its state medical assistance plan any state electing to meet Affordable Care Act (ACA) Medicaid expansion requirements under the Patient Protection and Affordable Care Act. Requires such bonuses to be in amounts made available from a net reduction in federal payments to other states not electing to meet those requirements.