Goal 9 of the Sustainable Development Goals aims to provide universal affordable broadband globally by 2030. However, a lack of data, combined with few independent and scientifically reproducible assessments, makes it challenging for governments to make strategic choices to achieve this target. Therefore, new research approaches are required to support decision evaluation. This paper demonstrates an innovative method that addresses data and model uncertainty by developing open-source software to explore affordable universal broadband strategies, using a scenario-based hypothetical mobile operator. Targets being considered by the United Nations' Broadband Commission are evaluated, with the financial costs of different infrastructure decisions quantified for the whole of Africa. The results suggest that "leapfrogging" to 4G is more cost efficient than 3G for providing universal broadband, with savings between 7 and 57 percent for 10 gigabytes per month and between 20 and 47 percent for 30 gigabytes per month. Moreover, the cost of connecting all unconnected and underserved users across Africa can be reduced by approximately 40 percent by targeting a per user consumption rate of 10 gigabytes per month, compared to 30 gigabytes per month. Future research should also aim to consider demand-side impacts, for example, how device affordability may affect adoption.