Chap here used to put his C of A aircraft in for its annual.
Often took more than four weeks, and the bill was often around £6k.
All for around 40 hours a year.
He sold it for about 12K!
He now owns a Permit to Fly, LAA-type that has retractable undercarriage, wibly prop and does 140kts in the cruise.
And costs, probably, about 1k a year to maintain!
Most of the blame is EASA (building on UK CAA previous, it must be said).
ps. Ten years ago, there were three aircraft here: two microlights and one C of A. Now there are 34 aircraft, and not one on a C of A. Perhaps that says most of it (although, it is true, we are not ideal for many C of A aircraft)