Shop with a blind eye to the pricing. Just get what you love. The problem is most of the time we love the most expensive option. Go figure. :)

If you are talking about glass subway tiles as in the image below (ie tiles made of glass), the pricing is usually in the backing. Sometimes the glue seeps through and leaves nasty "blobs" behind the glass. So you really need to talk with your supplier and even see examples if you can....

Somewhat attributable to thickness of glass too. When we were looking for backsplash tile for our kitchen renovation (12" x 12" mosaic) sheets we saw prices from $4 - $30 a sq. ft. We had just about decided that we were going to have to spend more to get what we liked (as Darzy states) when my wife found the perfect one and best of all it was only $5 sq. ft.