I would offer them the deal for 4 months with the option to get the same deal for the next 8 months. In the first 4 months they won't be getting a great deal but in the second and third periods they would be getting a really good deal since you would have more traffic and so there would be more value for them

Example: 1st Period (4 months) @ $100 with a total of 4k views based on 1k per month. Avg 2.5 cents per view.

2nd period (4 months) @ $100 with a total of 8k views based on 2k per month. Avg 1.25 cents per view.

3rd period (4 months) @ $100 with a total of 12k views based on 2k per month. .Avg 0.8 cents per view.

They would not be obligated to purchase the 2nd or 3rd period but I would make sure they have to make that decision 15 days prior to the end of period 1.

I hope this helps you. Feel free to contact me for more details. I have done ad sales from $100 to $50k ad contracts.