I have been running ½ an AA5B. It was costing me about 9K a year. In the process of selling shares, so expect this to come down to 4.5k for 1/5th. That is assuming I only manage 65 hours a year when I only have 1/5 of the aircraft.
Medium term plan is to run a Europa or similar aircraft, which I will own outright and expect to operate at about the same 4.5k cost. Main difference is fuel cost per hour. The AA5B uses about £40 an hour in fuel but the Europa will operate on £12 an hour at the same speed.
Rod