What would the bonus be for Lightning bolt once per day?

[Dormammu]

On a weapon? I'm thinking+1? Does something like this exist already?

[gooddragon1]

On a weapon? I'm thinking+1? Does something like this exist already?

Well, to just tack it on using the creation rules (http://www.d20srd.org/srd/magicItems/creatingMagicItems.htm):

3*5*2000=30000
Divided by 5 due to 1 charge per day, +6000 gp to add it on.

So it's noat a +1 bonus, it's just a solid gold increase in cost. This is not unheard of for items (armor does this (http://www.d20srd.org/srd/magicItems/magicArmor.htm), and so do some psionic weapons (http://www.d20srd.org/srd/psionic/items/weapons.htm) in the SRD).

[Urpriest]

It probably wouldn't, since it's not interesting enough or weapon-themed enough for someone to decide to make it.