Calculating After-Tax Cost of Debt for ABC Corporation

ABC Corporation has a debt of $10 million with a coupon rate of 6%, maturing in 10 years. The company is currently rated 'A-' by a major rating agency, and the yield on similarly rated bonds in the market is 4%. Additionally, the company is subject to a tax rate of 30% on its revenues. To incentivize additional investment, ABC Corporation is exploring refinancing options to lower its cost of debt.

Based on this information, what would be the estimated after-tax cost of debt for ABC Corporation?