SMS: A table that describes exactly the cost per SMS (price per character, and more)

Going to my view log, I noticed that some SMS cost $0.85 (not the $0.00085 advertised) and that some cost up to $5.10c.
I reached support to ask why that is, and they told me it has to do with the number of characters.
I asked for a table to understand how many characters we can use without going over 5x the base price, or the cost of each SMS plans would be (Marketing), but there is none.

It's a bit unreal that we just can't know how much it will cost to send SMS messages.
How come there is no table? What can we use as a reference to calculate costs, or to see if the SMS are being charged properly?

Absolutely not clear.