I've seen posts on forums talking about estimated prices for commissions on humanoid models and animalistic models, but I haven't seen anything about mechs in particular. Are fully rigged and textured mechs on average more expensive to commission than rigged and textured humanoid models because of the complexity of them?…
More complexity of work work cost more. So the rates you found for a humanoid would not be the same for the mecha your describing. As for rigging it depends on the needs but should be the same unless you need some specialties.