There is, of course, one simple modification that could be made to the targeting system that would render even the venerable SA-2 pretty impervious to ECM.
GPS for general targeting, then optical sensors for the final run. Sure, the guy laser painting the target would probably be caught in the blast himself, but Iran and North Korea have plenty of volunteers for that.
PS - the title is very misleading. Implies something put together out of scrap metal and good wishes.