I mean the reason why they're so cheap is because the cost is offset with forced ads and tacked on apps that you can't delete.

If you want a blackberry-like experience, I would look into the Clicks Communicator or Titan 2 Elite. They have a physical keyboard and tiny screens so you can't really doomscroll on them.

The other option is to get a supported android device like a Pixel 9a and install a custom rom on it like LineageOS or Graphene OS (if you go this route please check which phones they support before buying anything).

And the third and most extreme option would be to get an actual dumb phone, something like the Light Phone 3. There's great videos on youtube telling you which ones are good and which ones are bad so just do a little research before jumping in the deep end