as saint said you know your other side is working so trying the bits from the working light on the one thats not as in swap the bulbs first then swap the ecu's over ,if still no light but the other one lights then you know its the striker inside,don't know how much headlights are but think the strikers are around £100 , as for the old ballast I would have tried it on the other light to make sure it was knackered , but it might be worth getting a 2nd hand headlight with some short gaurantee .

again just out of interest how much did he charge for a bulb and the ballast ? if you don't mind telling