How can I efficiently access a particular game object's script's member variables from within another script?

I know this question sounds like a duplicate but I really have looked around already, and if you read on you'll see I'm aware of at least one method but want to know of others.

What is the best way to manipulate a variable within a specific game object’s script? I’ve learned that the problem with setting the variable to ‘public static’ and accessing the variable using ‘exampleScript.desiredVariable’ is that a static member acts as a universal member for the class, whereas I need to access a unique value for a given instance of that script.

The one method I am aware of is creating a new variable of the type ‘exampleScript’ within the script that would like to access ‘desiredVariable,’ because I can then assign a particular game object’s script to this variable and access and modify the members of the particular script by modifying members of the variable.

But what else is there? I am a little concerned that this is going to use up unnecessary space. Why create a new variable which contains all the data of MonoBehaviour plus whatever variables and methods I have written in the script, when that data (presumably) exists somewhere on the RAM already? Is there no way to access it without creating a duplicate instance? Is this as unnecessarily wasteful as I’m thinking it is, or I overestimating the overhead involved here? Please help, and thanks in advance.