Your mechanic is correct, but so are you. The mechanic's suggestion of a Corolla is a safe bet, one that won't come back to bite him in the long run, but the other cars you mention are also worth considering. All are solid, generally reliable cars, although I would be cautious about recommending the Astra to you. Stick to the well-known Japanese brands and she won't go too far wrong.

YOU'RE right to be concerned because the higher the mileage the greater the chances of major problems. Your car has done almost twice the average ks for a car of its age, so you need to be wary. The Mazda 323 is generally a robust and reliable car and I wouldn't be concerned if it had the average 150,000km or so. Make sure it has been serviced by the book, with regular oil and filter changes, and it should have had two cam belt changes by now. When you start the engine listen for any rattling, and watch for smoke from the exhaust. When you drive make sure the gears engage smoothly without any baulking, and that there are no noises from the gearbox. If you're not sure have a trusted mechanic check it, or the RACV if you don't have anyone you feel you can trust.