Bunnings is offering the Handy Shelf 4 Shelf Boltless Unit for $25 down from the regular price of $59.
The shelves are comprised of particle board which is very good for storing heavy items and generally is a solid storage shelf. I have a similar model to this one and I also have the cheapo all metal shelves. The metal shelves, while they do the job, are a bit flimsy and you just have to be a bit more careful of loading.
You also don't have to screw anything in. Should just assemble by hammer or mallet.
The Warehouse has a similar model for $79. That's rated for 150kg per shelf so a bit more durable. Mitre 10 has something similar for the same price.
Unit holds up to 200kg evenly distributed
Fully adjustable 9mm particle board shelves
Each shelf can hold up to 50kg evenly distributed
Plastic floor protectors
Easy to assemble no nuts or bolts required