new pak >> zis but they cost the same. No reason for that. It must be at least 450-500 mp for pak with stun ablility.
A unit which has a high received accuracy and dies with the loss of three models. The zis has the same received accuracy problem, but it dies with the loss of five. Additionally, as wehrmacht, this high price can destroy your map presence, and can be easily decrewed and stolen. Less importantly, PAKs are locked behind more tech and their stun ability is locked behind veterancy.