Why does the buy-in sit outside the annual math?
Because unlike rent, it is not consumed. A sensibly bought airframe holds much of its value, so the buy-in is capital parked, not money spent. The honest comparison is annual cost against annual cost, with the capital shown separately so you can judge what tying it up is worth to you.
What if I split ownership three ways?
Divide the buy-in and monthly fixed costs by your number of partners and run it again - the hourly cost stays the same. Shares are how most pilots beat the break-even line years earlier, which is rather the point of Resyrv.
What hides in the fixed costs?
Hangar or tie-down, insurance, database subscriptions, the annual inspection amortized monthly, and the quiet stuff: registration, cowl plugs, the GPS card nobody remembers agreeing to. Owners consistently underestimate this line; renters never see it.