From my Pacific Coast (Portland to Sacramento area) tour in 2008, roughly 1100 miles and 27 days, $41.74 per day, pretty close to a dollar per bike mile:
$125.00 - Amtrak
$320.22 - Motels (6 nights)
$420.00 - Groceries, camp fuel, beer/wine and misc supplies
$114.71 - Dining out
$ 50.00 - Bike Repairs (shifter)
$ 97.00 - Campgrounds (21 nights)
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$1126.93 - Total

No records from my other tours. In all cases they could have been less expensive than they were if I had really tried, but my focus wasn't on minimizing expenses beyond a reasonable amount. Some treats along the way are worth it for me (occasional motels, some dining out, etc.).