I hear you. You just asked how to get it off...

Those are tight... I pull them off with impact sockets and high power impacts.. If that doesn't work I put a pipe on my 2 ft long breaker bar. I have actually snapped those heads off those in a rust belt here.
Being in CA, at least you wont have to worry its is rusted together. Look on the bright side. ;-)
I am not sure harbor freight will have them.. they might. Home depot has 6 point wrenches gear wrench 14 piece kit for $53.38 (probably different pricing around the country)
Looking like 18, 19mm is the largest wrench in that particular kit. Some auto parts stores like you rent or buy and return tools too..