Just about any machine shop can insert a heli-coil for you and the cost should not be all that great. The whole process would take me less than ten minutes to complete. The amount of material removed would be minimal but the crank would still be a touch weaker. However...

Don't waste your time or money doing this unless the crank in question is a valuable one. Something of more entry level nature should be set aside and replaced with an undamaged crank.

Hope this is a help.