I would ask to see the last 5 years worth of maintenance bills on the one you are interested in and if possible the other 2 your mechanic looks after. This will give you a feeling for what you will need to spend to keep the aircraft.
The other thing I would recommend is that you talk to your insurance broker first. A low time pilot with no instrument rating on an airplane considered a hotrod will be expensive. An Initial course at SIMCOM (5-7 K) and the requirement for considerable dual before you can fly on your own will likely be required (50 hrs dual is not uncommon) and I would not be surprised if your premium quadruples over what you are paying for your Aero Commander.