So based on how fitting the business is for ads on your site and how good the click through rate is, i would come up with a fix monthly payment which can be reconsiderd every few month if something changed
Its hard to guess without more information but 1000 impressions i would say are worth around 3-5$ at maximum i suppose maybe even just, lets take 3$ that would be around 180$ for the ad
I guess you have mostly revisting user , so i suppose they would pay for the same impressions again and again . I would include google ads, more fitting ads for your visitors and because of that a better cpc and you still should have space to include the local ad