How would I go about determining a fair value for advertising on this page? I’m assuming the ad position would be replacing the existing google banner towards the top of the page.
Think about this user’s business. Estimate some reasonable CTR and conversion rate (1%/5%?), and figure out how much they might earn from having that ad on your page. Then take 10% of that and call it your price, if it comes out to something you’d find reasonable. Your best bet of keeping a direct advertiser will be to provide more value than what they pay you over time.
Well I would start by throwing out a number higher than what you think it is worth. See if the person bites and go from there. You can always come down, but never up.