Omnivaluation

Everything has a price.
You can literally price it in your local coinage.

You can and should price it. You should price it according to your own preference schedule, not the market price, for the purposes of comparing it to everything else. The prices won't be precise, and that's okay, as long as they're vaguely accurate. 

Or price it against gold or BTC. I'm not picky. You could price it against barrels of water if you really wanted to, but it seems like unnecessary work. 

When something is "priceless" either it is a fancy way of saying value = $0 or someone is trying to scam you. E.g. when they say "you can't put a price on life" it's both. They're saying actually your life = $0 and they want to buy your life at that price.
Price everything, so you learn better and don't sell. 

 

The scholar caste, and sophists in particular, don't like you putting prices on things because that's merchant behaviour. How dare you uphold the customs or habits of the "wrong" caste. Then warriors come along and say stuff like "usury is bad" because they keep taking out scam loans since they're neither well-learned nor into accounting...

P.S. Obvious thing is obvious, but if your own price is higher than market price, then buy, if lower than market price, then sell. Pareto optimization.