ECU failure after S80 engine replacement
 

My daughter has a 2003 S80 with 131,000 miles. It stopped running as she was driving at 65MPH on the interstate. I has it towed to a trusted mechanic, where he diagnosed a broken timing belt. Upon opening, he found the belt not broken but several teeth had sheared and it apparently slipped. As a number of valves were bent, we decided an engine swap was the most economical way to proceed. I found a good used engine, and he installed it. When the job was completed, the car started immediately, but quit after 30 or so seconds with the check engine light coming on. A read showed the code for ECU failure. I am advised that a used ECU is not an option due to the programming? A new ECU is $1300, which blows me away. Do I have any options? Should I try to get the ECU from the car from which the replacement engine came? This is my first exposure to an ECU failure, and I am mystified! HELP, please.