Following the lead of commercial satellite service companies, the Department of Defense is developing new Low Earth orbit (LEO) megaconstellations to improve the resilience and agility of military space systems. Megaconstellations can have hundreds of satellites in multiple orbital planes ranging from 500 kilometers to 1,200 kilometers in altitude. Additional replenishment satellites are maintained on the ground, ready to launch to replace satellites lost due to planned de-orbits, reliability issues, or attrition due to natural or manmade causes. DOD planning purposes demand a clear understanding of the cost implications for developing, procuring, and operationalizing a LEO-based megaconstellation’s ground system and satellites, including initial launch and replenishment costs. This paper describes robust and simple parametric cost models, with reasonable explanatory and predictive power, that we developed to estimate the costs of these megaconstellations using data from 12 LEO government and commercial constellations.