You can get a perfectly good slide rule for $20 or so from ebay. The expensive ones tend to have a bunch of extra scales that generally do things that are typically rare use cases and much easier to do on a computer. The basic C, D, A, B, and CI scales will do multiplication, division, squares, and square roots. K scale allows you to calculate cubes and cube roots.
They’re neat devices, pleasant to use, and the more complex ones are works of functional art. And there are some cases I find where their limitation to 2-3 significant digits helps me avoid getting buried in unachievable precision. But barring a global collapse there’s really no reason to use one other than you just want to.
