Mike, exactly.
Aircraft valued for fair market value, zero-timed, at 30K. Since then 1000 hours flown, meaning 15.000 in the engine fund. If everything (particularly the engine fund uplift) has been predicted correctly, the airframe (with its 1000 hour engine) should now be worth 15K on the open market, meaning the total assets of the group are still 30K.
A share in the group should cost 15K airframe + 15K engine fund divided by the number of shares.
Unfortunately most light aircraft are bought with emotion rather than reason and not every buyer does this calculation properly.