Or...are you invaluable?

I was writing some recommendations and started to say the person's input was "valuable," but then changed it to "invaluable." It made me think. Why is it that "invaluable" is so much better than "valuable?"

You can put a price on something that is just "valuable". If it's "invaluable" it's priceless.

You sound like a Master Card commercial.

Would that make fantabulous priceless, too? Or is it just a little more than fabulous?

That's just a portmanteau between fantastic/fantasy and fabulous. I don't think there's any implication of value included in the meaning.

invaluable

I read the in- in this word as the same one in inflammable: an intensive prefix, not meaning not but very. But, then, I see that same prefix in irregardless. Along these lines, why is priceless positive, but worthless not? And, what about without price? Is it that worth is intrinsic, but price is set from without?