There comes a point of critical mass with this game- at the very very top- where you get a sort of snowball effect with your resources. The players at the top spend very little on events, because they have the ridiculous teams that you can only theorycraft about that let them win with very little overhead. If you are only losing 1-2 pvp matches per event, you can easily get a lethal with a few hundred mags and a couple ps, meaning you make hundreds of selling the lethal.
In one or two months of that, plus event rares, plus a few decent trades, and you could have thousands of resources sitting around. That is pretty much where those players are. I was there too, at one point, so I know how it can happen. It starts building pretty quickly once you get there. I was scraping and saving for 9 months, then all of a sudden in one or two I suddenly had 900 ac in my account that I didn't even remember getting.
I scaled down considerably from there, and now am in a position just below that point, where I can still do reasonably well without large expenses, but like in everything in our world, the rich get richer and the poor get poorer. For a free player to break into that level, you are looking at at least 4-5 months of hard and smart playing, with very few mistakes. Ask Legend, he has been doing it since coming back as a free player. Albeit he has had his reputuation in the game to give him so leverage which has helped, but he went from pretty much scratch to running for lethals in about 3-4 months.