In the past you could build a reasonable one for $200-$300. When "we" were growing up - consoles used to offer huge performance at a tremendous discount. For instance the video card in the original XBox was worth significantly more than the entire system's retail cost. But that era ended at the PS4. Consoles since then are sold with midrange hardware, derivative of typical retail hardware, sold for or near profit on day 1. Beyond this fact, their prices tend to stay fairly comparable to launch prices even as the price of hardware plummets. And now a days we've apparently entered the era of their prices going up relative to launch prices lol.

So the most expensive, and important, by far on both accounts part of a decent gaming PC is the video card. A PS5 is around an RX 6700 or a NVidia 2080, and that's being generous. That's a ~$300 card. You then have $300 left for case + mobo + CPU + RAM, which isn't hard. And in reality your CPU doesn't really matter (within reason) because in modern times basically 0 games are CPU limited. It's pretty much always the GPU. Work out the minimum amount you can get the non-GPU parts from, use your remaining budget on the GPU - you'll end up with a great machine for easily under $600.

There's a bunch of subreddits dedicated to this exact topic as well. /buildapcforme could be nice for more specific advice. In general I'd recommend against buying prebuilt systems. The markup they charge is unreasonably high and 'building' a PC in modern times is basically legos for adults, and there's about a million videos on YouTube showing you exactly what to do, step by step.