The answer is not as simple as you think it is. Each manufacturer will select what they consider to be their basic specification model and set a price for it. Unless the specifications are the same then you cannot really compare one make with another unless you try to value each component.
Unless a company is ordering in significant numbers per year then they will not be getting a manufacturer prompted discount, they will be relying upon what the dealer can offer. What the dealer will offer will depend on what he has either in stock or on order. This will vary from one town to another and one dealer group to another for the same spec vehicle.
The remaining life of a particular model line, or a particular specification will have a considerable influence upon ultimate sale price, particularly when someone is left with stocks of the superseded model. In that instance their higher spec vehicle may well be cheaper than another’s base model.
You will possibly find that any simple, fairly uninformed opinion-based answer can conclude that either Iveco or Renault will be the cheapest advertised price, with that being based upon perceived reputation. Trailer prices will be again dependent on specification, the larger companies who order will be not just deciding which tyre they want fitted, but whose axles and brakes are used; even for the supposedly bog standard 13.6 metre curtainsider.
This post a short while ago referred to a long term vehicle comparison test carried out in Germany which did try to come to a slightly different conclusion. This may help to explain why there is no simple answer to your question and why purchase price is only a minor factor in the equation.