I haven't actually stayed Deluxe yet, but I'm hoping to do a split stay with four nights at AKL on my next WDW trip and funding-wise it looks feasible. I work in a mid-size museum in a small city with low cost of living; I'm not rich by any means but I live comfortably. I'm not going to sit here and say that anyone can afford Deluxe if they just try hard enough; I personally know people who would struggle to afford a stay in a WDW Value. There is definitely a baseline income you have to have before it's feasible; I don't know exactly where that is. As for how I afford it on the salary of an employee of a nonprofit....
I have a very clear budget and vacation savings are a big priority with every paycheck. I use You Need a Budget to track everything; I spent a year just tracking what was coming in and what was going out so I would understand where my money was going, and then built a budget based on that. The big things it does for me is that a.) I always have money set aside for recurring expenses and emergencies, so those don't wipe out my discretionary funds; b.) I'm able to cap my spending on indulgent categories that don't matter as much to me in the long term view, like fast food (I have a really bad fast food habit, but I'm improving!); and c.) I'm able to budget enough for the things I do want to have available to me that I don't feel deprived.
That last one was a big one that kind of surprised me. In that year of self-observation, I learned that I'm much more likely to break the rules I've set out for myself if I feel deprived. It may seem counter-intuitive, but I found that by increasing my budget in a few categories (entertainment, clothing, and home goods were the big ones) I decreased my overall spending in those categories. What was happening was that I'd hit my spending limit, get frustrated, ignore my budget, and go way over. Now that my budget is more generous in those areas, I always feel like I have enough and often don't bother to spend it all. So if I had $15 per paycheck in one category before but would routinely break the rules and spend $50 from it that I had to scramble to cover with other funds, budgeting $35 is actually cheaper in the long run when that's an amount I can stick to.
I was also very fortunate in that I got a substantial raise about a month after "finalizing" my budget (it's never really final; I constantly tweak it). When the raise started coming in I simply did not increase my spending in any of my regular categories. All of that money got routed straight into my vacation fund, and continues to go there. That helped a lot. By never giving myself a chance to grow accustomed to spending all of my new, higher salary on day to day life, I've never had cause to miss that money.
Then there's just various ways of saving money. I own a house, but I co-own it with a friend. I walk to work every other day partly for my health and partly because it means I can fill my car's gas tank just once a month, sometimes even less frequently than that. I deduct all of my donations; we've been KonMari'ing the house and it's shocking how much of a deduction I've been able to get off of my state taxes just by reporting the things I was already going to donate. The KonMari approach means I'm also much more stingy about buying new things; I only buy things that perfectly suit my needs and whenever it's practical I wait for sales instead of buying things right away.
And then when it comes to vacation, I build thorough and honest budgets for each one before I go. I skew the numbers high on everything so that I'm more likely to underspend than overspend based on my expectations. I figure out what I can afford, and I spend just that--no more coming home from vacation to two months' worth of credit card debt.
And finally...others have said it, but I'll reiterate: I've just started to be able to do this kind of vacation now that I'm in my early thirties, and tbqh the only reason I can afford to do it so early in life is that I don't have kids.
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