Lou -- there are fixed costs (hangar, insurance, mortgage if needed)
and variable costs. The fixed costs are easy. The variable are not.

Variable:
fuel & oil
repairs, maintenance,improvements
ADs
Unexpected and surprising costs!

And, as Jay points out, you can do a fair amount of work (Preventive
Maintenance, as per the FAA) yourself. But then you need to make sure
you have tools and equipment to do this. More costs.

On the other hand, if you really total up and make realistic estimates
of a budget, you'll probably decide not to buy an airplane.

*sigh*