A 1st level spell that duplicates an 11th level feat for 1 round.
Since you're so set in going by the guidelines, you should note that they're also intended to be compared to other items, even before you price with those guidelines.
30k for an 11th level ability is cheap when you can spend 25k to get a 2nd level ability (Evasion).
EDIT: By your interpretation, a continuous True Strike effect would still be that 8000gp. +20 to attack, by itself, is worth 400,000gp.