I would say cost depends on what is on offer, for a time Morrisons did kits for less than ã7 a can, at Christmas I got kits from Tesco you order on line and collect from shop so no postage, Wilko do deals I got some kits at ã10 each, even local brew shop often sells of out of date stuff cheap.
There is nothing to stop you growing your own grain, spreading it out on the floor get it damp and malt it and really brew from scratch. However each stage you go to needs more space, and likley more equipment, I use cans as I have not got the space, I am sure my brother-in-law living in an old farm house with out buildings could brew from scratch. But the other thing when brewing from scratch is quanty, there is little diffrence in the work involved to do 40 gallons or 40 pints, and most farms back in the 17th centry would brew once a year and that beer would last the year. However I want to brew smaller quanties and all year around.
Brewing all year around means temperature control which bumps up the price. You could start a brew today and you would not need any temperature control, it's the right time of year, but next month it will be getting too cold and last month it was too hot.
I find temperature control a problem, brew in the house and it works quite well, the central heating means it does not get too cold, and the mass of the house also stops it getting too hot, OK a little hit and miss, and the brew time varies due to temperature, but in general it works OK.
Once you move from the house the normal thing is to create a mini enviroment for the brewing, in a box, (fridge etc.) because the box is small the brewing will heat it up, so with the fridge example the temperature outside the fridge needs to be lower than 16ðC or you have to turn the fridge on to keep it cool. My idea of heat only did not work, I expect you could have a fan to cool when required, but once out of the house keeping the temperature correct in real terms needs heating and cooling. So once you exceed the 40 pints that will fit into a fridge everything gets more complex.
So the answer as to cost is linked to:
How much room you have.
What offers you can take advantage of.
What you want to pay to set it all up.
There is also what quality you want, using simple sugar you can use one can kits to make a cheap beer. To improve quality you need to move to 2 can kits. As you prograss to tailoring to your requirements you return to one can kits with non sugar fermentables. Add the cost of dried malt and a one can kit is more expensive than a two can kit.
Where the kit is good is you can get the same results time after time, assuming temperature contol is used, so you can add things and know the diffrence is due to what you have added, not due to diffrent batch of grain, slighlty more time on heat, and all the other varibles. So you can learn what a can of treacle can do, or a jar of honey, or any other, I found by accident orange works well. You have a stable base to work with.
You can also experiment with higher alcohol beers, I found sugar produces an off taste, however charcoal will remove the off taste, so my next experiment is to make some sugar alcohol then remove the off taste, then either add flavors to the alcohol or add it to beers to lift the ABV without adding off taste. It may be a failure, but until I try I will not know.
I mix in the kitchen, and clean in the kitchen, everything else is done in garage or shed the latter is where it is all stored. so 40 pints is about my limit to carry from kitchen to garage so that's my limit for brewing.
