First off: You should ask your GM if he is ok with you creating custom magic items before presenting gold coin formulae to him.
You cannot create effects that are instantaneous as permanent, it's the same discussion about a sword of striking true or infinite healing potion.
The permanent version of such effects are the enhancement bonus and special effects that work based on enhancement bonus (Fire, Frost, Shock, Keen, Vorpal, etc).
If you read the note on continuous effect you will see that there is no Instantaneous listed on it, meaning you can't do it.
If a continuous item has an effect based on a spell with a duration measured in rounds, multiply the cost by 4. If the duration of the spell is 1 minute/level, multiply the cost by 2, and if the duration is 10 minutes/level, multiply the cost by 1.5. If the spell has a 24-hour duration or greater, divide the cost in half.
You can, however, make a sword that allows you to cast shocking grasp a couple times per day at caster level 5. The cost for that would be (5 * 1 * 2000)/ (5/5) or 10,000 gp.
The cost was based on the following formulae:
- Use-activated or continuous: Spell level x caster level x 2,000 gp
- Charges per day: Divide by (5 divided by charges per day)
You still would have to add +1 enhancement bonus before adding any special effect, and that extra effect should probably cost 50% more for being something normally available to wondrous items. But that is entirely up to your GM.
See how a 5 times per day item costs the same as what you tried to do but is infinitely inferior?
Even if you had your sword of shocking grasp, activating a spell trigger item is a Standard Action, meaning you would have to stop for a turn, activate the Shocking Grasp ability, deliver the spell with a free Touch Attack as part of the spell effect, and the next round you would attack with your sword but with no shocking effect because the spell does not allow you to do that.
You would have to be a Magus to accomplish what you are trying to do.
You are better off making a +1 keen shocking burst sword.
- +1 enhancement (necessary for any further effects)
- +1 keen (enhance critical range to 17-20)
- +2 shocking burst (1d6 eletricity damage on a hit, 1d10 on a critical)
Total +4, or 16,0000 gp.