My question is in the title of this post, and I do not know what else to say. I am just puzzled.
Okay, to avoid my post being put on hold for being too succinct, I will add a couple of naive thoughts of mine.
I originally thought that "моя дорогая Наташа" means something along the line, "Natasha, I know that you are not cheap and that I consequently have to pay a big price to continue getting nice treatment, attention, favors, and other things from you." Or maybe something like this: "Natasha, I spent so much time, effort, and money to make you my woman; you proved to be really expensive." But the very idea that people could talk to a woman in terms of her price seems nonsensical to me, as any normal woman would get offended.
Then it came to my mind that the Russians who call women "дорогая" may mix up price and value. But I cannot imagine someone mixing up them. Only most uneducated simpletons who completely lack common sense are capable of mixing up these fundamentally different things.
My naive thoughts seem both nonsensical and funny to me, so I am puzzled.
Could you explain?
UPDATE
Reading answers, I realized I had to better explain the source of my confusion and my motivation to ask the question.
Of course, I am well aware that when the adjective "дорогой" describes a person, it is usually perceived as "dear" and not as "expensive."
The source of my confusion is that when the Russians speak about material things, they use the adjective "дорогой" to say that the thing is expensive or pricey, and the adjective "ценный" to say that the thing is valuable or useful. For example, дорогой инструмент is an expensive or pricey tool (not necessarily useful), and ценный инструмент is a tool that is valuable or useful (not necessarily expensive). To make sure everyone understands me, "expensive" is about the price and means that you pay a lot to buy the thing, whilst "useful" is about the value and means that you derive a great benefit by using the thing.
What is beyond my understanding is why the Russians chose the word "дорогой" (which, as I explained, is about the price, not about the value) as the Russian word for "dear."
I never saw English speakers writing something like, "He has a dear car." Typing in Google the exact phrase "has a dear car," I get only 1 result. I know that English speakers can occasionally say, "The price is too dear," but in this phrase the word "price" is explicitly said. Anyway, English is not my native language either, and my question is about Russian, not English.
It is beyond my understanding how the Russians can use one and the same adjective, "дорогой," to say that a thing is expensive and that a person is dear. I know that many words have more than one meaning, but all meanings of one and the same word are logically connected unless we talk about homonyms. And I cannot see a logical connection between "expensive" and "dear." The latter two words cause very different emotions and associations.
Moreover, I found in Google that the expression "дорогой сотрудник" can mean a dear employee and an expensive employee, depending on the context. It is astonishing how one and the same Russian expression can be perceived in so different ways.
What adds to my confusion is that the Russian words for "price" and "value" have the same root (-цен-) and are, respectively, "цена" and "ценность." This is beyond my understanding.
In short, I feel there may be some fundamental differences between me and the Russians in how we perceive economic processes and interpersonal relationships. This was my primary motivation to ask the question. My primary interest is to better understand the Russian way of thinking.