The place to get stainless stock pots in Melbourne is SPRINGVALE.
Yep, I wandered down to have a look. For those Melburnians not familiar with Springvale, there are three stainless steel pot vendors (that I saw) in the area bordered by the train line in the North, Windsor Ave in the South, St Johns Ave in the West and Buckingham Ave in the East.
There are three distinct quality levels for stainless steel pots, each with a different price.
Inside the Springvale shopping centre (between St Johns and Buckingham Aves) are the cheapest pots. They have sizes from 36l up to several hundred litres. The 50l pots (labelled '40cm') are $75 if I recall correctly. These pots are made from such thin steel that they are often not round (distorted into an oval shape at the top) and the bottoms need a ridge pressed into them to give them enough strength.
Some of the pots on show had cracks and scratches. The handles were roughly spot-welded on, and green corrosion (copper?) could be seen on the welds. Generally the workmanship looked poor, but what do you expect for that money?
The other two shops were closer to the train line. One shop had mid-range pots in various sizes, with 50l pots for $150. These pots had thicker steel and flat bottoms. The thickness was the same for the walls and the bottom. These were not heavy pots, but they were obviously better than the $75 version.
Workmanship was OK except for the rivets holding the handles on. They didn't go all the way through (only 3/4 of the rivet head made it through the wall) so they could be expected to fail sooner or later and would need to be re-riveted.
The last shop had the highest quality pots. A 50l pot was $220. These pots were heavy, marked 18/10 grade stainless steel and with thick bases. Workmanship looked flawless.
I have seen pots of this standard for $300 at catering suppliers, so their pricing is OK given the quality.
So there you go, you get what you pay for when shopping in Springvale! Thanks for the tip Chimera.