Welcome SCTSCT,
Biggest diff you prob find here is the cost of boats is high and 2nd hand boats even higher (comparatively). Unfortunately unlike the US where boats seem to almost halve in value when you drive them out of the showroom, they really hold their value here. Desirable 2nd hand boats hold their value to such a degree that you virtually sell them for purchase price (except extras) years down the track.
I have owned a number of boats starting from tinnies, plate alloy and then several glass boats. Personally I wouldnt own a alloy boat anymore unless weight was a huge factor (traveling offroad to NT etc). So cant really help with choice of alloy boats. When the Aus $ was higher quite a few guys here imported US boats (I imported a Grady White for a mate). There may be some US alloy boats around the 2nd hand market.
The $30k budget should get you something reasonable but prob restrict you to smaller or 2nd hand.
Good luck.