Let's break this sentence down:
Prepositional phrases are marked between parentheses: The only car (for him) is one (of those new GTOś.) Notice that prepositional phrases always include a preposition such as for and of, and its object as in him.
The subject is The only car.
The verb within the sentence is is.
There is only one complement which is the subject complement: one of those new GTO's. Remember that the subject compliment gives us more information about the subject and it usually occurs after linking verbs (seem, be, become), which in this case the linking verb is is.