If these people are new to the hobby and they’re not flippers†, then they’re using their hard earned money from their day job.
A bit of selection bias here - just because you see big boys like smpratte, gary, and cullers buying and selling $25k+ items with a collection behind them worth 6-7 figures doesn’t mean Pokemon always pays for itself. These are the top flippers, ahem, dealers in the hobby, and the time and cash they’ve poured into the hobby for the past 10-20-30 years isn’t something that you’re privy to. They didn’t just arrive at the top, they’ve been working their ass off since they started.
The average user on this forum is not cash positive from this hobby. Meaning, if you calculate Cashsales - Cashpurchases, the vast majority of users here will have a negative result. Now, it’s very possible that the market value of their collection compared to the amount they’ve spent far exceeds what they paid for the cards, but what I’m trying to get at is that the collection only ‘pays for itself’ when you’ve made more from selling cards than you’ve spent purchasing cards. And for 90+% (I’d wager) of collectors here, that just isn’t the case.
Even when you want to start getting into the flipping side of things, you’re going to have to spend money to make money. Buy low, sell high. You can’t sell before you buy.
In effect, your question is, how do I successfully buy and sell Pokemon cards so that I’ll be able to make enough money to pay for the cards that I want to collect? And unfortunately, the first rule of that all flippers must adhere to in order to survive and profit is that you never talk in detail about your flipping strategies. Not where to buy, not how to buy, not when to buy, nada. Nothing personnel, kid. Remember the amount of time I mentioned that smpratte et al had to go through in order to get to where they are? This is part of that. The information’s out there. The flipping opportunities are out there. But you won’t find them (or, honestly, even get remotely close to them) without putting in hundreds and thousands of hours of initial research and then an ungodly amount of ongoing effort to actually find and be available to the opportunities when they arrive.
† - Flipper, card dealer - same thing. Someone that sells something for more than they bought it for, on a routine basis and as a way to make money, is a flipper.