The same sentence could be translated as you suggested, but the nuance changes.
~でしょう isn't used in this case because it sounds too definite. It changes the feeling from "I'd like to do x, but the conditions of y are not favorable" into something more declarative ("I will do x, once y is becomes a reality").
The final けど is a softener. It is very much like the sentence ending of "but" used by people from some English-speaking countries (particularly Ireland.) It is just a device used to soften the end of a sentence, and to segue to the next thought. So whereas your ~でしょう implies the speaker will absolutely buy a car when/if the money comes in, the sentence in the Genki example implies that the speaker would probably buy a car if some money comes in.
The explanatory の is explained elsewhere on this site and in other places.