Peugeot is almost the only option for a diesel small/medium car for that price range.. Citroen (reliability?) and Holden Astra/Vectra also did diesel but aren't many around. May be able to find a MkIV VW Golf oil burner in that price bracket as well if you're lucky.
If it was up to me I would go a Peugeot 406 or 306 diesel, best suits open road driving, good reliability and not boring to drive. Super frugal as well. Maybe do a bit of time looking around aussiefrogs.com if you want to research it more.

