Unfortunately, you will not have the scale to sell to national advertisers for some time. This means that you will have to sell to local advertisers. Selling local advertising is very expensive because you are going to have to talk with each or your customers and they all are going to want to know “will you guarantee results”. I would team up with some one that specializes in local advertising, like a pennysaver and see if they would be interested in reaching out to their customers.
However, I haven’t answered your question. To be honest, I don’t think there is a standard price. It will depend on how much local advertisers perceive to be value and the results they get after they run a test campaign.