re your calculations on pricing repair vs new above: Andrew's list 10" primaries on their site for $499
http://www.andrewscom.com.au/site-section-10.htm
(scroll down a fair way)
Since they sell the GSO dobs I am making a bit of a leap by assuming that these mirrors are also GSO, but if so they are quoted as being 1/12th wave accurate (see the dobs description further up the same page), however I'm fairly certain they are bare aluminium and not Silicon Oxide overcoated.
Worth the price of a phone call perhaps, if it gets to that stage?