What an interesting and diverse thread, with some excellent comments and views....
Here's my thinking on the various aspects of our game. I know some will disagree with some of it, but it's just my way of approaching the cost of our hobby.
Like any hobby, scale model building is as cheap or expensive as you care to make it. Spare dosh being, obviously, the main consideration.
I was taught modelling by my late father, and in those days modelling airbrushes, pigments ect. and all the after market stuff was unheard of, so we had to get on with what we had....Airfix models, paint, turps, school pastels and a pencil. That was it!
I still only use the same stuff today, and as I don't possess or want an a.b., my modelling costs are minimal.
As folks know, my dioramas are more or less built for free. I use scrap and unwanted packaging (in my Omaha dios, the bunkers were made of plant trays and a cut in half plastic flower pot!) I state this to show what can be used and for nothing. So dio's can be built with little expense or for free...... It just needs a bit of scrounging and though.
I generally buy the cheaper kits such as Academy and ICM. I see these kits are usually looked on as 'Inferior' in some folks eyes, who see expensive Tamiya as the only kits worth a carrot. Most cheaper kits can be turned into a finished model on a par with 'Better quality' kits......Who wants drop together kits anyway, we are modellers are we not?lol
I agree with Derek and others on the subject of aftermarket stuff....I avoid it, full stop! Even if I had the spare cash, I wouldn't but any of it. How can the crazy, over the top prices be justified? I just don't see such a great improvement in the finished model to justify spending an amount which is usually way over the top of the original kit cost! I'm more than happy with my

.b. models.....And the money saved buys me another kit!
Buying washes and various pigments for this and that are not really neccessary. I've seen some great models on here using cheap alternative methods, such as childrens pastels to achieve the same results as expensive pigments ect.
Modelling can, and in my case is, dirt cheap. The kits, a few paints and scrounger's instincts are all I need.
I'm not knocking those who do buy all the stuff going, I just know it's not neccessary to have all the clobber to produce satisfying models.....
In conclusion, we all have our own ways of achieving the desired end result. If one has an endless supply of spare pennies, that's fine, buy away......But spare a thought for others at the other end of the scale who don't have (or want) that luxury and have great fun model on a shoestring.
Irrespective of what we have or want from our modelling, the one thing money, or lack of, can't buy is FUN!
Cheers all,
Ron