I wouldn't say it's all that popular, I don't know anyone who drinks it. tbh I think your average Joe Bloggs drinks the cheap local 4% ales like Speights, Waikato Draight, Lion Red, DB Draught etc, then you've got local beers like Monteiths and Macs, and then you've got the international lager staples like Becks, Heineken and Stella. Steinlager is in the latter category but I honestly don't know anyone who drinks it instead of those mentioned.
Having said that, it's certainly not perceived as a cheap beer, it's in a similar price bracket to Heineken or Becks, maybe a dollar or two cheaper. And they recently released a new version called "Steinlager Pure" which I have had a few times and am quite partial to actually.
Another related question- I regularly drink Becks or Heineken, and last night I bought a dozen Stellas home for the boys (they were on special at the supermarket) and they ridiculed me and claimed it was common knowledge that Stella was awful and I may as well have bought 20 Double Browns for $20 as they wouldn't taste any worse. Anyone else agree that Stella is awful and of a lower calibre than Heineken or Becks?