As mentioned already, you would need to make the weapon +1 to start with. See dmg pg 223 under the Magic Weapon Special Ability Descriptions header. Also, if you look at the special weapons with non-standard abilities (sun blade, sleep arrow, etc), those also have some sort of +X in addition to their special abiltiies.
And as Vahktang pointed out:
Vahktang said:
Why stop there?
Just pay the full 2315 and have it True Strike with every hit.
Good luck getting past your GM though.
...
True strike shouldn't be added to anything.
Except maybe a wand.
More later,
Vahktang
As noted in the sidebar on pg 282 of the DMG, the formulas are only a starting point. True Strike has a significant inherent limitation in that it is a personal spell. Placing it in a magic item bypasses that limitation. Making it command word also bypasses the AoO a spellcaster would normally suffer for casting it in melee. With those things in mind, I'd treat True Strike in a weapon as a 3rd or 4th level spell for price calculations to reflect its true value. That would get you a price more like 15,120 plus the value of a +1 weapon (2k) for a total price of 17,120.
Note that a true strike command word ability with no limitations on use per day built under this formula would still be only 75,600. Compare that to a +6 weapon. The true strike weapon gives a much higher bonus to hit than the +6 weapon, but doesn't gives a bonus on every attack in an iterative group and doesn't require a round to activate. You'd probably have to playtest the two to see if they were equivalent (as you should probably playtest the once per day true strike weapon against the similarly priced +3 weapon)
Edit: Also, compre the correct version of the weapon by the DMG formula as calculated by Pyrex treating True Strike as a first level spell against a +1 or +2 weapon to see if the power level is correct for the price. My intuition is that the +1 w/true strike weapon is at least as good as, if not better than, a vanilla +2 weapon, and should therefore be priced accordingly.