The term "affordable" and "affordability" are bantered around a lot on audio forums and in product reviews, but of all the terms in the lexicon of audio jargon, "affordability" is probably among the least well-defined words.
From the onset "affordable" is very much a relative term. What was "affordable" for me when I was 30 is quite different from affordable now that I've passed 60. Or has it? Sure, I can spend more money now, but in terms of my overall income, relative "affordability" might not have changed much.
Since affordability is such a personal matter, demarcating "affordability" with a particular dollar limit makes little sense. While a $1000 component might be quite affordable for some audiophiles, others might find even this too expensive. Perhaps a better way to measure "affordability" is with a mathematical formula? Oh No! Math...
What if we choose a percentage of total income as a demarcation of affordability? For argument's sake let's arbitrarily choose one week's salary or 1/52nd of a year's salary as "affordable." For someone making $52,000 per year that would be exactly $1000, while for someone with a $104,000 salary that would get bumped up to $2000. For that $1000 you could put together a very decent headphone system for connecting to your computer or smartphone or an entry-level home audio system using some new and some used components.
At a certain salary level everything becomes affordable (hello oligarch audio), but even if you only have a budget of $1000 per year, after ten years you will have a killer system, not only because you've spent $10,000, but because you've had ten years to do your homework. And when you set a yearly audio budget, you don't have to spend it each year, you could save up a couple of year's worth and then buy something more expensive, but still, since you've stayed on budget, affordable.
Now I know there are some audiophiles who don't and won't feel like they're fully committed to their hobby unless they overspend to the point of eating Ramen every day, but a more rational and less extreme approach makes more sense for most audiophiles and will bring far more long-term pleasure. It's hard to enjoy the music when your credit cards are maxed out and the next payment is due in two days...
I don't expect the term "affordability" to gain an absolute definition anytime soon. But that doesn't mean you can't develop your own personal terms for affordability. Devote a set yearly percentage of your income to audio that you can afford to spend on audio without denying other financial responsibilities; stick with it, and all your gear will be "affordable." Simple? Yes?