Launch cost per kilogram is the primary metric for comparing the economic efficiency of launch vehicles, calculated by dividing the total launch price by the payload mass delivered to a given orbit (usually LEO). The Space Shuttle era saw costs of roughly $50,000-60,000/kg to LEO. Falcon 9 reusability brought this below $3,000/kg, and Starship aims for $100-200/kg at full operational cadence with complete reusability.
This dramatic cost reduction is the single most important enabler of the modern space economy. Lower launch costs make previously uneconomical missions viable: mega-constellations, in-space manufacturing, space tourism, and large-scale orbital infrastructure all depend on affordable access to orbit. The industry is approaching a threshold where the cost of launch becomes a small fraction of total mission cost, shifting the bottleneck from access to orbit to what you do once you are there.