A new ecu for 700$ is about right, however I would not let them put one in. If they do, it will fry again and they wont cover the 700$. I say hit a u pull it and grab another ecu or two. Swap it in and drive strait back to the dealer? Then see what they say? They need it running to diagnose, so get it running for them.

88 Montero, StarQuest turbo, Kormex 5speed +tuff-pan w/phoenix f. stage2 clutch, 4in lift+33' tires, 4.875 lsd, short-throw shifter, Aisin hubs, SR big brakes, gen2 uca's, elantra alt, and so much more... 16g turbo w/hardpipes + 4.90 locking disk-brake axle soon (maybe lsd or aussie front??)