The most valuable resource in Magic finance isn't money-it's time.
Have you ever played one of those worker placement board games where one of your early moves end up paying off massive dividends a dozen turns later? One chicken turns into two, which turn into four, which turn into eight, which eventually trigger a secret condition that allows you to upgrade your coop into a plutonium powered research facility. All you have to do is wait long enough and your investment does all the work for you.
There are real-world analogies for this type of game. You know those older folks who tell you that your 401k will be worth, like, a LOT more at retirement age if you start paying in when you're still in your twenties as opposed to waiting until your mid-thirties? Believe it or not, they're actually onto something. (Though by "something" I don't mean "an accurate understanding of the financial realities facing younger generations.") As it turns out, investments tend to grow exponentially over time-the more money you invest, the more it grows, and then the growth can be reinvested, and then THAT growth can be reinvested, and on, and on, and on.
Magic finance is no exception to this rule. In 2002, Underground Sea was $20. In 2012, Scalding Tarn was $12. In 2014, Snapcaster Mage was $18. In 2016, Collective Brutality was $2. You didn't have to be rich to buy these cards and reap a massive profit, you just had to be patient.