Greetings,
After reading your project description, I am very glad to let you know that I have taken interest in it. I am a proficient content writer and researcher with many years of experience, and I have previously done several jobs quite identical to the one that you have posted. Assuming that you may have a lot of ads which need to be posted, I believe that a price tag of $600 is fair enough given the fact that I would be working extremely hard on this project in order to have everything done for you as soon as possible, while of course also maintaining top quality.
I am also very interested into communicating closely with you, in order to make sure that all work is done based on your liking. Also, from what I understand this would be an ongoing project, which is fine for me, as I would also be interested in working with you on a long term if needed.
I am looking forward to hearing from you soon, and hopefully start working on your project as soon as possible!