User:Evil4Zerggin/Return on investment
A regular pop costs between 25 and 100 base Food to grow at a food surplus of 1. Past 1 food surplus marginal growth drops by a factor of 10, making the marginal cost per regular pop greater than that for robots. They consume a base upkeep of 1 Food.
Regular pops are therefore fairly cheap if grown at resource-optimal rate, even when farm quantization is taken into account. If we figure an average surplus of ~2 Food, the effective cost of a pop is perhaps 50 to 100 Food, comparable to a station. But they are quite slow to build at this rate. Still, they are competitive with stations on good natural tiles.
Robots cost 150 Energy and 50 minerals, and consume a upkeep of 1 Energy---a greater upfront cost but arguably a lower cost in the long term. The main advantage rather appears to be their flexibility.
Each level of a resource building costs 30 minerals more than the last, and generally increases output by 1 and upkeep by 1/2. Assuming no natural resources are suppressed, the first two levels are a good deal, with the first being cheap and the second not costing additional upkeep. But after that I would build stations first.