Free and very cheap tax advice follows:
Unless you do a lot of hours - I'd go with the hourly rate, a comparable hourly rate if you had to hire the same plane from someone (long as you consider $ value / residual value of plane, no instructor wages etc)
Not really defensible charging $ 400 / hour for a 'flying flea' ...................... I wouldn't think
Not really defensible if plane costs you $ 15k per year to insure, house, fix and run and you only did 10 hours and 4 hours of that was business - Mr tax commissioner would take a very dim view of a deduction of 4 hours @ $ 1,500 = $ 6,000
(there would probably be an entirely different argument if the plane was 100 % business and owned 100 % by a business)