Its not to hard for a shop to do, but if you are using the stock crank, it will require mallory, which is a bit spendy. You could make an argument that the stock cast iron crank is not worth the effort. However, if you do balance it, you would be well served to also machine the crank to radius all the journals as well to eliminate potential stress points.
If you are using an aftermarket cast steel or forged steel crank, then its a whole 'nuther ball game.