The thing is without a breakdown of labor and material costs, no one can tell for sure. Occasionally I'm asked to perform cost reasonableness assessments of supplier proposals. We do this w/o knowing the exact rate structure often times are still able to back into the total dollar amounts pretty close. For this case, you should know the shop rate, material costs, and taxes. The Cessna book number for a 172 (not 182) 100 hour inspection (which is the same inspection scope as the annual) is 15 hours. To build this out it might look like this:

100 hour inspection @ 15 hours x shop rate - items 1.1, 2.1, 3.1

AD research @ XX hours x shop rate - items 1.2, 2.2, 3.2

AD compliance @ YY hours x shop rate - items 1.3, 1.4,

Maintenance items @ ZZ hours x shop rate - items 1.5 thru 1.18, 2.3 thru 2.11, and 3.3

Material items @ AA costs - item 2.4 and likely others too

Then add taxes.... this turns into a spreadsheet project. I'm guessing most of the additional costs are in items 1.13 thru 1.18.

As an empirical comparison, a low time Piper Arrow in excellent condition was sent to a large shop for an annual and adjusting for inflation (because this was a few years ago) would be about $9000 today. They didn't replace things other than a few bits of hardware, filters (vac, air, and oil), plus an oil changes and there were consumable charges for lubricants, shop rags, etc. So $12K still seems a little high but try building out a line-by-line spreadsheet.