Okay, so I just happened across Ordained Champion's and Spellsword's Channel Spell. Now, before you tell me that these and the abuses are known, or that Ordained Champion got errata-nerfed, I searched the forum and the specific issue I found is not mentioned.
Specifically... you don't cast the spell. You channel it into your weapon, spending the spell slot ("as if you had cast the spell"), and then you poke something with the weapon and it goes off. This bypasses material and XP components.
Ordained Champion's errata-nerf does cut down on the abuses of this, since most cleric spells with material and XP components have long casting times, but it doesn't remove it entirely.