My point, which you more or less make in your last paragraph, is that what study materials you have doesn't matter as much as your approach to using them does.
One person can spend $10,000 on lessons from GM's over the course of a year, and another might spend $2,000 on books/dvd's in a year, while a third spends nothing at all and just studies games on chessgames.com or a similar site.
The results of those three people will have nothing to do with how much was spent, and everything to do with how much effort was given.
This is all a matter of perspective anyway. For example, someone with $1,000 of disposable income per month will see prices and value a lot differently that someone with $1,000 per year of disposable income.
At the age of almost 40 and with a relatively well paying job I personally find a huge value in lessons with a coach. I also spend several hundred dollars a year on books and DVD's.
But when I was 18 years old and just starting out in the workforce with only a few bucks here and there I would very carefully make my selections and buy only a few used books here and there.
I also made great use of the public library. I would go there on an afternoon when I wasn't working and copy down games and notes into a spiral bound notebook. I'd sit at a table in the back with a pocket chess set for hours just going over game after game.
So is any given book/dvd course worth $X? Just depends on what you have to spend. The key is to maximize what you do have. It's not the book/dvd, it's how you use them.
Hey i know a couple rich people. They will a dollar out of 15 cents. They can walk inside a mall and get the same things but find it cheaper. Think they will not go to thrigt store? Wrong.
I have expensive taste but when it comes to chess i am cheap. The only thing i will serios money on is 1 Marble Chess Set. Over 60% of my chess refrences is free. I have a few chess books. And i have to say that if any beginner sat down with them for 2-3 months they would be difficult to beat. That is how i pick my books, to make a big impact.
For me why spend more than $50 which is real hi for me. If is like a car when it leaves the car lot. As more people buy the book does not lose its value. If you and your opponent have been reading this same book it has increased the chance of a draw. That same book is closer being worth $50 when your opponent has no knowledge of its content or your one of first to buy it and use against opponents. Hey i would not even want somebody to spend too much money buying that book for my B day or Christmas. Back to the store it must go.
Now on things like good food, clothing, music and etc i will open up my pockets if i have everything else taken care of like bills and etc. I spent about $100 on a pair of jeans once. Then went inside some of the most expensive stores to find a few shirts to go with it. Not just to spend it. They had to quality. I had went to over 8 stores and 5 Malls to finish shopping.
You say it is how you use them. I play Vote Chess and ideas can change quick. A line of attack can work great for while then it is found out it may no work as well anymore. Recently i had to dump 2 different lines of attack with the same opening from a book. Have another that i can not use as it is avoided by my opponents lately. For the most i have great books and get the opportunity to use 90% of it.