Hey, I'm also in Adelaide, and drive my '03 172 to work every day. Do around 50km per day.
Regular maintenance is the key. The engines are strong if well kept, however other items will wear out just as much as on any other car. Rubbers on a car of that age/mileage will probably be up for replacement. Think Engine mounts, suspension bushes. Suspension may also need to be done as the shocks might be worn out.
Also, the rear wheel bearings are known to be a weak point on these - but that is a pretty minor issue.
Probably the biggest ($ value wise) issue likely to come up is the clutch. If it has already been done then you should be right, but at 200k, it will be nearing the end of its life. Fairly big (time consuming) job - which is where the cost is - parts aren't too expensive.
However, if you are willing to do some of your own maintenance, or keep a service budget, that will be handy.
What you save on low purchase price you can spend on keeping it running.
Oh - and running costs - I use around 8L/100km fuel (95/98 RON) going across town (NE to Airport). 15" tyres are around $120-135ea, so pretty affordable.