3 years into this ownership game I would advise anybody buying an aircraft to ensure that whatever they buy has the avionics on board that they will be happy with until they sell the aircraft and that it all works. FM immune nav radios is a fairly useful place to start and if you want a GPS in the panel, buy an aircraft that has one in already!! The costs involved in upgrading this stuff make the day to day maintenance costs look a bit incidental.
If I were buying another second-hand aircraft now I would also be quite attracted to a high time engine in a lowish time airframe and to get the engine replaced or overhauled early on. Mine was a mid-time engine so it had had around 1200 hours of who knows what sort of use. Although it checked out fine on the pre-purchase inspection it started 'making metal' after no more than 100 hours and I had to have it replaced. I'm not sure I'd be that impressed with a very low time engine either since you would have no idea how well it was run in.
Mine is an Arrow so if you want to talk further about the real running costs do get in touch.