It’s a lot more than $100 extra. A standard 250 litre unit is a bit over $800 and a stainless steel one will set you back nearly $1200.
Just had a look at pricing on my Reece account.
Rheem 250l 3.6kw S/Steel single element - $1,373.00 incl GST
Everhot 250l 3.6kw S/Steel single element - $1,373.00 incl GST
Rheem 250l 3.6kw glass lined steel cyl single element - $1,278.50 incl GST
Everhot 250l 3.6kw glass lined steel cyl single element - $1,094.00 incl GST
Dux Proflo 250l 3.6kw glass lined steel cyl single element - $1,311.50 incl GST
Thermann 250l 3.6kw glass lined steel cyl single element - $1,072.00 incl GST
Almost forgot Aquamax which is another brand from the Rheem stable
Aquamax 250l 3.6kw glass lined steel cyl single element - $1,298.00 incl GST
All prices have been rounded.
Cannot find any price listings for DUX or Thermann 250 litre stainless steel models however I may just not be using the correct key words in the search engine.