Forget about the Volvo S40, it's not that well built and drives like a sponge.
I don't disrespect your own opinion,
but I drive a 1999 VW Golf GTI Turbo and...
... a 2004 Volvo S40 T4 2.0 Sport!
I can't really comment on the standard S40 because mine is a T4.
But I will say that they are quite well made and mine is bloody fast.
0-60mph is about 7.4 seconds,
Top speed is 150mph(ish).
It handles well and gives plenty of four door comfort.
My Golf on the other hand...
Well I don't need to tell you about that one.
Any thing you guys would recommed for max $10,000AUD
You could do much worse than a Volvo.
I was quite impressed by the 2002/3 V8 Commodore SS I drove last year on hols.
If you're not bothered about how many doors it's got I saw a very nice 1993 Honda Prelude (2.2ltr V-Tech Low on Insurance but still fast) for just over $8000AUD. You might be able to find something similar. Just because the Japanese engines are smaller, don't let it put you off, they're still quick.
Good Luck!