Look at a Greater rod of Quicken. Quicken is a +4 spell level feat. So quickening a 9th level spell with it allows you to, in effect, cast a 13th level spell 3 times per day. The greater rod of Quicken costs 170,000 GP and in effect allows you to cast 3 13th level spells per day.

Persistent Spell is a +7 spell level feat. Persistent Spell combined with a 6th level spell uses a 13th level slot.