I remember the first time I heard this, I was in a book store in Mexico looking for a Spanish dictionary. Oddly enough, I had a hard time finding a pure Spanish dictionary at home. But I digress.
I took my dictionary to the counter and asked "¿cuánto cuesta?" just like my Spanish book taught me. That's when the attendant looked at me and said "¿cuánto vale?" Then she proceeded to tell me the price of the book.
At first I thought I said something wrong and found myself pretty confused for a few seconds. Luckily it wasn't hard to figure out what it meant, but I was stuck with the feelings of confusion and doubt until I got back home and my Spanish tutor got me all straightened out.
It turns out that "¿cuánto vale?" is just another way to ask the price of something. It's used universally, not just in Mexico, so you're likely to hear it somewhere down the line.
There are a few other ways to ask the price of something, so let's take a quick look at them.
How much does that come out to?
How much is it?
¿Cuánto le debo?
How much do I owe you?
Since we're on the subject, I talked about costar before, and you can click here to read about that. It's used in a very common expression and has a another usage that you definitely want to know about, so be sure to take a moment and look over that post.