1999 Mitsubishi Eclipse Guarantee Reversed.

I took my car in to Midas 4 days ago, complaining of leaking antifreeze, and my temerature gauge was going really hot. That same day, Midas called me and said that I needed a new radiator and one of the motor mounts had broken and needed replacing. I asked how much for each job and was quoted $800 for the radiator and another $500 for the motor mount repair. I hesitated, at first asking him to only replace the radiator, but he told me, "Ma'am, if you fix both of these, now, I guarantee your car will be in tip-top condition. You'll be ready for a cross-country trip, in no time. This sounded great, so I told him go ahead and repair everything. When I got my car back, the next day, the same guy who told me of the "guarantee" told me it was odd, but they couldn't figure out why my car temp wass now fluctuating, going from extreme hot to below average in seconds. And, that the car probably needed a head change. I asked him aboutthe guarantee and he walked away and got the mechanic to come back and tell me the same thing he had just said. And, that this might cost somewhere between 400 and 2000 dollars. I am appalled at this. Do I have any recourse, and of course, what could be my problem, after all? I feel like I've been ripped off, and now my idle revs on its own, and it's never dne that before. Also seems like my fan is late to turn on and cool the temp gauge (which was changed, by the way), and my belts were all changed. Help?