In my view it would not be particularly difficult to fix by a good TV repair person.
As you are asking this question I am assuming you are not a technical person familar with TV circuits. A good TV repair person should be able to trace the fault in a couple of hours, but intermittent faults are often difficult because quite often when you take the back off the set and it does not fail.
If you get a B&O dealer to repair the Beovision, then they will change the whole board depending on its age, so will be more expensive.