I agree that the verbs in the following are monotransitive (taking only one object) and in the passive form. (The doer is not indicated. But for purposes of this discussion, let's just say the subject is "they.")
Costs were discounted at 3.5% per year.
(If converted to the active form: They discounted the costs at 3.5% per year.)
Only one object: costs.
The annual number of unique warts episodes was estimated at about 156 000.
(If converted to the active form: They estimated the annual number of unique warts episodes at about 156,000.)
Only one object: annual number of unique warts episodes.
But I think the verb "have" in the "Incremental benefits...." sentence may be more complex transitive than it is ditransitive.
A complex transitive verb takes an object plus a complement or an adverbial. Examples:
He got Jenny upset.
(Subj verb direct obj complement)
Elaine laid the flowers on the table.
(Subj verb direct obj adverbial)
A ditransitive verb takes an indirect object and direct object as in the ff. example:
I gave Belinda some biscuits.
(Subj Verb Indirect Obj Dir Obj)
I gave some biscuits to Belinda.
(Subj Verb Dir Obj Indirect Obj)
Thus, in the following sentence, the labels could be:
Incremental benefits of... do not have a large effect on the cost differential.
Subject verb direct obj adverbial