//Materials for a brew cost me between $65 and $100 for a 19 litre batch.
Ouch, that is extreme, do you mean the stainless brewing vessels and so on are part of that formula?
No, just ingredients. Grain, hops and any other additions needed. Sometimes includes yeast, sometimes not. Yeast can add another $12-$20 or so.
Here's an example;
Get close to the equivalent of 5 dozen from that, so even if I work on 4 1/2 dozen then retail that's about $200 at an average of $22 a 6 pack, so I'm saving 50-65% off retail.