I had a C172 for a while. When asked how much per hour it cost my reply was my first hour in a year costs about $8000 and my last about $40. This included heated hangar, insurance, annual, etc.

300 hours of dual in the same airplane would not look good at all unless it was student pilot => CPL. You can't just log unlimited dual just "because". There are many legit reasons for dual (refresher, BFR, IPC, club checkout, insurance checkout, aircraft fam, area fam, route fam, etc) but very few other than certs/ratings can justify much more than 10-20 hours at the most.

The only legal way to share and log unlimited amounts of time is hood/safety pilot. Even then the SP cannot log the entire flight (subtract taxi, T/O, LDG) and can never log XC.

Yeah, but is it legal flight time? Example, CFII gives 300 hours hood instruction to another rated pilot or CFI gives 500 hours of dual instruction towards an ATP rating to another rated pilot? Basically, two pilots buy a Cessna 150 together and they fly it together to build total flight time. One of the owners happens to be a CFI.