The dwarf wood scorpions of Asia and the Pacific, flat, small, mild, and carrying the single most market-defining trait a scorpion can have: parthenogenesis, in the widespread species, where one female becomes a colony unassisted.
Crevice-dwelling, humid, communal, and about as low-risk as the order offers. They fit setups nothing else fits and thrive on neglect.
Parthenogenesis caps prices permanently, because every kept female produces surplus and any scarcity is temporary by construction. A starter animal is a one-time purchase and an escape is potentially a population, which are the same fact viewed from two directions. The genus is infrastructure, honestly priced as such.