OBJECTIVE: Airborne infection from aerosolized SARS-CoV-2 poses an economic challenge for businesses without existing heating, ventilation, and air conditioning (HVAC) systems. The Environmental Protection Agency notes that standalone units may be used in areas without existing HVAC systems, but the cost and effectiveness of standalone units has not been evaluated. STUDY DESIGN: Cost-effectiveness analysis with Monte Carlo simulation and aerosol transmission modeling. METHODS: We built a probabilistic decision-analytic model in a Monte Carlo simulation that examines aerosol transmission of SARS-CoV-2 in an indoor space. As a base case study, we built a model that simulated a poorly ventilated indoor 1000 square foot restaurant and the range of Covid-19 prevalence of actively infectious cases (best-case: 0.1%, base-case: 2%, and worst-case: 3%) and vaccination rates (best-case: 90%, base-case: 70%, and worst-case: 0%) in New York City. We evaluated the cost-effectiveness of improving ventilation rate to 12 air changes per hour (ACH), the equivalent of hospital-grade filtration systems used in emergency departments. We also provide a customizable online tool that allows the user to change model parameters. RESULTS: All 3 scenarios resulted in a net cost-savings and infections averted. For the base-case scenario, improving ventilation to 12 ACH was associated with 54 [95% Credible Interval (CrI): 29-86] aerosol infections averted over 1 year, producing an estimated cost savings of $152,701 (95% CrI: $80,663, $249,501) and 1.35 (95% CrI: 0.72, 2.24) quality-adjusted life years (QALYs) gained. CONCLUSIONS: It is cost-effective to improve indoor ventilation in small businesses in older buildings that lack HVAC systems during the pandemic.