make him your slave with a limited wish you quickened thanks to your lesser quicken metamagic rod he forged himself for a measly 17500gp).
Wouldn't that be impossible? Limited Wish is a seventh level spell and lesser metamagic rods only work on 3rd level spells and lower.
Plus it'd be a pretty poor use of limited wish if you knew the exact spell you'd want to duplicate with it. Limited Wish has a material component that runs 1.5k gp in order to duplicate the effects of a 4th-6th level spell which makes it about as expensive ... as making a 5th - 6th level scroll outright. You'd get a slightly better Save DC I suppose?
DGMW, Limited Wish is an AMAZING spell if you are in a situation where you really, really could use a specific spell that you never thought you would need but do. But if your plan involves scrying, it probably involves knowing what you are facing. In most cases, it would be cheaper to just prepare the spells you expect to use.
Honestly, these discussions always involve levels I rarely reach in a campaign, in any edition. My gut feeling is that a GM that takes a group from 1st to 13th knows the system well enough to create challenges that aren't easily solved with one assassination attempt.
Edit: Murphry's Law