OK, so which is the expensive lens?

Haha. This thread is hilarious.

Depending on the situation, it can be tricky to tell the difference between a pro lens and a consumer one.
However, I find this totally wrong for long focals. Take a look at sport images that you see in the magazines. For most of them, it is purely impossible to take the same picture wih a consumer zoom. Compare a Canon 70-300 or a third party equivalent to a 300 2.8 L and you can tell the difference from Mars.

If you're rich -ans silly- enough, you might buy L lenses for showing off, but you can also buy L glass (or high end equivalent from 3rd parties) because it allows you to get pictures you CAN'T get with non-pro lenses.
This is particularly true if you want a fast telephoto lens.

Hard to determine since 1 is over exposed and 2 is close focused, ie. not focused on the crown stamp on the lid.