Integrated classified ads and shopping cart needed

We want to have a classified ads section on our news site, with the option to charge for posting ads. Ideally, we'd like to be able to let local folks post for free, and just charge big companies or out-of-towners.

So far, I have had no luck finding a plugin combo that does this. I suppose we could use a non-WP system and just link to it, but I'd rather stay within the WP framework, naturally.