I help my AP with the annual and if everything is pretty good and doesn’t require a lot of extra stuff it runs about $900, pretty reasonable.
Yep, the airframe inspection time is mostly pulling insp panels and interior, and putting it all back.
Porsche was determined to use distributors instead of mags on the Cessna 172 project. That required two batteries, two alternators, and two wiring harnesses that could be cris crossed at the buss bar if an alternator on one side, and a battery on the other side happened to fail.
For weight and balance, the batteries were mounted in the luggage compartment. The layout also required larger fuel lines and an electric fuel pump and filter mounted under the floor. The stuff crammed under that floor was ridiculous.
Very smooth running engine with a belt driven fan for consistant cooling, and twice as many hours before overhaul. Burned a couple less GPH (iirc). But the conversion added 70 pounds to the plane. The airframe was zero timed, with new windshield, etc.,plus new interior and new paint.
Porsche got the STC approved then shelved it. It was too expensive. Buyers said they might as well just get a 182, and be able to go faster and haul more.