You could certainly use multiple themes in subdirectories as below:
e.g.
yourdomain.com <== Vantage
yourdomain.com/jobs <== JobRoller
yourdomain.com/classifieds <== ClassiPress
You also may want to make use of a
WordPress multisite installation for this purpose (more details in the link).
Each theme has its own settings, so yes if you were to make some kinds of listings free on Vantage for example, you can charge for ClassiPress listings etc..
If you're looking to purchase more than 2 themes, then the AppThemes club package would be the most economic option. You can read more about this on our
pricing page. Thanks.