you'd want to remove the head, drill the stripped hole out to a proper size for the insert (nice and straight.. a drill press would insure this) Then tap the new hole to fit the threaded repair-insert (which has to be chosen properly) Then an insert installation tool would be used to drive the insert in.. i left out a few details. the kit alone is gonna be about $30, probably more..
the part you could replace is the head, which might even be cheaper than doing it yourself.. but it seems like a no-brainer to pay someong to repair it for you if, as g.b. says, it can be done for under $20..