Yeah, at least if you are looking at new hardware, for roughly the cost of two RX 570s, you could instead get something like an RX 5600 XT, or maybe an RTX 2060.
A 5600 XT will typically be nearly twice as fast as a single RX 570, putting it on par with the best-case examples of what multi-card scaling could provide. And since most games don't scale nearly that well, the single faster card should provide significantly better performance in the majority of titles.
Plus, the 5600 XT is built on a newer, more efficient process, so it only draws around 150 watts under load. A single RX 570 draws more power than that for almost half the performance, and two of them combined are likely to draw around 350 watts when both are being heavily utilized. In addition to requiring a better PSU for the stable operation of that multi-card setup, it would also be dumping a correspondingly higher amount of heat into your case, potentially causing cooling issues.
And then there's the cost of electricity to factor in. As an example, at the current average price of electricity in the United States, if you were to game for 3 hours a day on average, the pair of RX 570s could cost upward of $25 more a year to run than the single 5600 XT, likely negating any potential cost savings (at least for whoever pays for the electricity).