I was comparing the cost for making "see invisibility" permanent (via permanency) to the cost of making a headband with continuous "see invisibility" on it. Is it a fair comparison? It seems that the cost of the headband would be 24,000 gold. For the spell it says the caster must expend just 5,000 gold. I guess that's not a bad markup for a wizard. To be honest, I am probably missing something.
You would loose your 5000 gp as soon as someone casts dispel magic on your permanent see invisibility. At worst you would only temporarily loose the use of your headband if the same thing happened to an item.