Found the Guitar Hero II "party pack" for Playstation 2 only with 2 wired guitars for $99 at JB Hifi Games and DVD store in Melbourne (366 Lonsdale Street, Melbourne 3000). Note that the other Melbourne city JB Hifi has it for $120 so I can't be sure it'll be available at other stores. Online seems to be around $140-$160.
It's the cheapest way to get into guitar hero, if you like that kinda thing. And the songs on Guitar Hero II are better than III in my opinion. Though if you want wireless guitars then this is not the deal for you (but you'll be paying a bunch more).
Just picked one up - once I get a second-hand PS2 I'll have a guitar hero setup for ~$200.