If you don't mind me asking, do you populate the initial listings on the job board by your self (by finding job listings and posting them), or leave it empty upon launch and just offer a period of free listing to get started?
I was populating the board with jobs for companies I scored recruiting contracts with.
These contracts made building the JobPosts and driving traffic worth my time(contract = collect a sizable a fee when someone you refer to a position gets hired).
JobPosts drive the organic traffic to JobBoards, so make sure you take SEO into consideration when posting.
I also started with a much lower rate to post on the JobBoard, never free, but as low as $29 at one point. As the traffic grew, so did the price. Now a JobPost costs $349.