I don't think that figure is correct, you need a "good heap" of GPUs, not just anything... in particular, even just to run inference, you need at least 400 GB of GPU memory, not just RAM. You can't just plug a dozen "cheap" GPUs and call it a day, because if I remember correctly consumer GPUs have at most 32GB of RAM each. Hence you'd need at least 12 of those top-tier GPUs (which certainly don't come at $500 a piece). Probably more, because you can't trivially split weights across GPUs so perfectly (you probably have to put an integer number of layers on each GPU).
In practice these models are typically run using top-tier A100 GPUs, which apparently is the cheapest thing you can do at scale: https://forum.effectivealtruism.org/posts/foptmf8C25TzJuit6/.... It looks like you can get away with just $10/hour, but I'm not sure I believe it. In one hour you can roughly generate 6 million English words this way, that's quite cheap.
But if you want to own the full hardware, then it's quite more expensive. You need 8 of those A100 GPUs, which come at $32k a piece, so you're in the ballpark of > $300k to build the server you need. Then there's of course running costs, these GPUs burn 250W a piece, plus the rest of the server we're at about 3kW power. That's not much, maybe $0.50/hr, plus maybe another $1/hr to cool the room it's in, depending on where it is (and the season, I guess in winter a fan might suffice, it's about as powerful as a couple small electric heaters). So with an upfront expense of > $300k, you're maybe down from $10/hr to $1.5/hr, saving something like $8.5/hr, which is $6k / month (minus the rent of whatever place you put the server in).
All in all, it's definitely feasible for a small start up as well, but not very much for an individual.