What's the most expensive skill/spell/sup/power you've ever spammed, %wise?

Most new magic and communes start expensive and get lots cheaper, some don't ever get much cheaper. Sometimes you just want that thing in the 90's at least now...and don't want to wait 3/4 levels foe it to start working well....

I think the hardest I've ever spammed was a 12% per cast spell. And since that pain, I think I've tried to intentionally wait till they were at least under 8%....but to behonest, I like to wait til they are less than 6%....but that's really almost never the case, it seems.

Anyone ever spammed something that expensive? More?