The cost (path and link) are only useful when there is more than one way to get back to the portal. What is striking about that output is link quality. It is in RSSI and you are right 10 is almost unusable. You should be getting at least 20.
How far apart are these devices?
How high are they mounted?
What terrain is between the devices?
Has this link ever been good?
Please check out the Point-to-Point application note here: http://www.arubanetworks.com/pdf/technology/AP_OutdoorPointToPoint.pdf