what would be the right price?

Hi everyone, I would like to have your opinion about this: What would be the price that a web designer should charge for making modifications to an existent drupal site, adding selling car ads that should be paid for to be published, payments would be made through paypal, additionaly, a report of the ads should be generated each week in pdf format, there would be a search system for the publish ads too different criteria (like model, etc).

I would really appreciate to hear some opinions about this, would like to know what would be the aprox cost of this, thanks in advance.