This is amazing: they must have placed a huge breaker bar on the wrench and tried to move it that way, breaking it in the process. Steel plugs so tend to weld themselves to AL heads, leading many people to use nickel antiseize and re-torque the plugs occasionally. The 100k plug may last that long, but you will have one hell of a time removing it.

Remove the head? If they have to drill through the plug, then probably so, since the chips will be deposited into the cylinder. Have them drill only part way in and try to use an Alden extractor or another reverse-out device to remove the plug. If this does not work, you are indeed going to have to remove the head. But 1300 pounds? Over here, the average independent mechanic would charge around $US700 for the job. They are asking three times that: too high. Find someone else.

By the way, do they have any liability in this instance? After all, they are the ones who broke off the plug body.