Tried to do some research on relative stocking costs of different species, but couldn't find a single site comparative price list. Collating info from several, it seems rainbow trout are the cheapest to stock at a catchable size of 8-10", while for example bass & walleye prices are comparable only at smaller fingerling size, catchable size double to triple that cost.
From experience, it seems trout are more likely to remain in a stock area than other species, advantageous to shorebound anglers particularly kids & less mobile seniors. Luckily, water bodies deemed suitable for other warm water species are managed for them when budgets permit. Kinda funny when you hear about dual cold-warm managed areas where the larger predators wait for the stocker trucks.