There's a lot more factors that go into this than just personal gil. If people just generate a lot of gil, that does make NPC costs trivial at best, but the price of things on the marketboards simply increase (Fun fact: This has happened over the course of ARR! Especially the introduction of duty roulette and challenge logs).

This is because money, when you boil it down, is simply a placeholder for goods and services. The notion of 5000 gil is meaningless without any context (and indeed, the worth of it differs from server to server.) Rather, a player is likely to think of gil in terms of "I can buy my next set of HQ armor for this much" or "A stack of my favorite food tends to be this much" or "I can craft these items, and they sell for this much." This is especially true when regarding whether something's worth the cost or not, it usually tends to be a simple matter of if it's easier to get the item themselves, or to do whatever farming method they prefer to produce the gil for it.

In this regard, I'd say what matters most is being self-sufficient. A good 100k is probably good enough to ignore most NPC costs, especially if you have crafting leveled to use dark matter for repairs over using repair NPCs... and especially if you turn in expert dungeon drops for GC seals for the dark matter and durability potions. Once you've got repairs and teleports out of the way, it's a simple matter of finding some source of income that produces more gil than you spend on food and potions. Whether that means using cheap (or no!) food and sticking to the idle methods of duty roulettes and ventures, or finding something to farm that suits your needs is a balance all up to the player.