Instead of $189/hr for emergency rates, not to mention the 1 week guarantee, (which I would be very careful offering this, I would seriously reconsider), I recommend charging a premium flat emergency fee and then your normal rate. With companies you have developed a relationship with; you could always negotiate a “monthly retainer” with x number of support hours, which in turn would give them a guaranteed response time from you. Instead of a premium rate for work performed after hours and weekends, you could have it use up the time at a higher rate – (i.e. – 1.5 hrs = 1hr ).
Just my .02˘