you can spend $100-$200/month and progress. You can spend less and progress slower, more and progress faster. If you want to start today and be endgame in a month, you can't do it. If you want to be endgame in a year, yeah you probably need $20-$30,000. But generally looking for decent event opportunities and spending during those is the better strategy to just blindly buying loot boxes. Myself and most people I know spent and made huge progress in the 2022 Slayer event. Problem with this game is it took over a year where there was no event to make significant progress in, just loot boxes.
They have decent $50 packs for newbies, but for some reason I can't really understand they only sell them when new updates go live. @Hermesput these on the store permanently, it's not like people only start playing during updates, the attempt at FOMO to boost sales is silly. Also repeat random newbie events, last year's heavenly enchant event for example helped lowbies, as did the lottery.
Add another $50 for blessed exalted enchants, and you're basically good to go to 110. From there yes, you have to spend some, grind some. At 112 you should be able to do IOS solo, that helps a lot. That's when you start needing prestige. You grind, you upgrade, that's how this game works.
I can do 150 bil/week (1 dk + 2 archers sharing gear) from TOI, there's people that do a lot more. If I had the time, I could probably do another 40-50 bill/week doing 3 hours of IOS a day/ 3 chars. But that has taken time, you can't turn up with an abandoned 99 level from 10 years ago and expect to do the same in a week.