I think in fairness it's an apples to oranges comparison.
How long will it take you to setup postgres on a VM and sort out and pay for somewhere to put backups? Let's say only a hour, and your time is worth say $30/hour you've just spent 6 months of planetscale fees and you've still got to pay your VPS and backup provider.
That's one way to look at it. I personally think it's worth burning a few hours to learn how to do something yourself even if you don't immediately get value out of it.
If you want apples to apples then Planetscale is compared to the ergonomics, pricing, and performance of the bests. If you want to compare you don’t analyze things in isolation by looking at your own expenses.
How long will it take you to setup postgres on a VM and sort out and pay for somewhere to put backups? Let's say only a hour, and your time is worth say $30/hour you've just spent 6 months of planetscale fees and you've still got to pay your VPS and backup provider.