Bids for Philly's Plan are coming in at and above the high end of the expected range: The Philadelphia municipal Wi-Fi plan calls for a non-profit to fundraise and take loans in order to fund residential wireless access for all at dial-up rates. The plan originally called for about $11 million in funding and $5 million in infrastructure paid from operating revenue; this is often reported as $16 million in funding, but it assumes excellent early revenue. And in this article, Philly CIO, Dianah Neff, says she was always talking about $15 to $18 million in "financing," so I'm not sure how that breaks down between funding and operating revenue.
The bids that have come in so far are in the $18 to $20 million range, and unnamed sources expect the cost to be at least $20 million. Since no one has built a Wi-Fi (mesh or otherwise) network of this scale before and no one operated it, it's all educated guesswork until the real obstacles appear.