Have you thought to contact DVLA and ask their advice…??
We have taken non-road-legal cars to and from UK, using a car-trailer, towed behind our personal car. Is this a possibility??
At the time it was certainly cheaper than sending via a Car Transporter.
Or… how about getting it CT’d and then drive it back to UK…after telling DVLA you are reimporting it to UK… ie no longer SORN.