First, a quick lesson in regards to tube/valve amp volume.
After a certain point, wattage does not necessarily represent volume. A 50 watt amp is much louder than a 15 watt amp, but a 100 watt amp isn't much louder than a 50 watt. Once you get into higher wattages the watts represent headroom more than volume. Headroom is the amp's ability to remain loud while clean.
When you pump up the amp's volume the power tubes eventually start to clip the signal, resulting in power tube distortion. You can think of power tube distortion as the tone of a cranked Marshall JTM or JMP. It's a little loose sounding with lots of mids, basically it's that crunchy Classic Rock tone. Higher watts means you can go louder before the signal clips. This is why the old Fenders that people use for clean tones are 65+ watts--they need to be high wattage to stay clean.
Most modern metal guitarists use 50+ watt amps (typically 100+) even if they don't need the loud cleans. This is because the tight and bassy distortion tones that modern metal is built upon is pre-amp tube distortion. Metal guitarists want to void power tube distortion because when combined with preamp distortion it flubs out the bass and gives the EQ a weird mid hump. Therefore a high wattage amp with lots of headroom will afford them the most volume with the least power tube distortion.
Now, being AUD really fucks thing up
Australia always gets screwed over with amp prices. Here's a few that might be in your price range:
Peavey 6505+ is one of the more common entry-level high gain tube amp heads. 120 watts, loosely based on the Soldano SLO 100 crunch circuit except with a more American voicing (meaning 6L6 tubes, flatter upper midrange, tighter bass response).
http://www.youtube.com/watch?v=1RT9Zce3fKs
Blackstar HT-100 is a 100w British high gain amp with circuitry based on the post-JCM900 Marshall amps. They have a bit more upper midrage and a rounder bass. They have a "voicing" control that alters the midrange curve to be more "british" or more "american" and as such is pretty versatile.
http://www.youtube.com/watch?v=Z_rWhL6IyIE
Krank Krankenstein Jr or Rev Pro Jr, 50 watt amps. I personally don't like them much but some do. I think Dimebag Darrell and Brendan Small (from Metalocalypse) both used Kranks at some point.
Rev Pro Jr 50 and
Krankenstein Jr 50.
Egnater Vengeance, 120 watt. American amp, lots of gain. A fairly new amp, only been on the market for a year or two. Half power switch (60w mode and 120w mode), independent EQs for both channels, built in reverb, and lots of switches for things like mid cuts and bass boosts.
http://www.youtube.com/watch?v=SD4MOWWJuqs&t=1m45s
Peavey 6534. Same as the 6505 except with EL34 tubes instead of 6L6s. Slightly more british flavor, looser bass, wider mid hump, warmer cleans.
http://www.youtube.com/watch?v=qmEnpwhfd80&t=2m1s
Marshall JVM205H. 50 watts, modern british tone. Some like, some don't. I actually like it but Marshalls are overpriced in the States, just listing it here in case Marshalls have fair prices in AU.
http://www.youtube.com/watch?v=FQDHzmmvDxA