Quote Originally Posted by Fax_Celestis View Post
Gravestrike, Golem strike, and Vine Strike (undead, constructs, and plants, respectively) can be applied as a continuous on-hit affect to a weapon for a mere 8000gp a piece, using the "use activated or continuous" entry.

The formula, as outlined in the DMG, for "use activated or continuous" is "Spell Level * Caster Level * 2000". Since the duration of the original spell is measured in rounds (1 round, to be precise), we multiply this cost by 4.

Plugging in, we end up with (1 * 1 * 2000 * 4). 8000 gp.
Remember to ask your DM though, because the same cost would be applied to continuous True Strike :)