What caused this insane inflation?
Gold available in game for farming.
More gold = more cash shop currency bought with it = higher bc price at exchange npc = higher prices of cash shop items.
This prices you can see now are not insane inflation. It is result of years of increasing gold income with incoming patches and level caps.
Real insane inflation was just before last patch. Devs add few quests with completely unbalanced gold reward with previous patch and gld/bc ratio doubled in less than a month. ?Last patch cut rewards from them and prices dropped to previos level in a week or 2.
Almost all endgame activities can give you some gold. If you want just "to survive" you actually doesn't need to do anything special. You need some effort if you want to improve. Most efficient way is some investment in reincarnations and repeating some most rewarding daily stuff with them.