Onshoring Essential Antibiotics Act This bill requires the Department of Health and Human Services (HHS) to provide grants to up to three manufacturers of essential generic antibiotic drugs (or of the active pharmaceutical ingredient or key starting material for such a drug). Under the bill, an essential generic antibiotic drug is one that HHS deems to be medically necessary to have available at all times in adequate amounts. These grants may be used to (1) construct, expand, or upgrade a manufacturing facility in the United States; and (2) manufacture essential generic antibiotic drugs. HHS shall commission a report with (1) recommendations about which drugs should be prioritized in the grant program, and (2) an analysis of the expected effect of domestic drug manufacturing on drug costs to consumers. HHS may stockpile essential generic antibiotic drugs manufactured in the United States. The bill provides in funding for the grant program and for HHS to stockpile generic antibiotic drugs.