Like their real life counterparts most are derived from road cars I've drawn. They are commonly referred to as LCVs (light commercial vehicles). Hopefully I will in due course find the time to draw some lorries.
For portraiture, cost is mostly related to how much livery and graphics needs to be drawn in. A blank, single coloured (not including black mudguard of vintage type) would be the same price as the road cars they're based on. Livery applied needs to be assessed for cost.