I'd think 200 to 300 sounds about right. But may be worth asking a few of the selling sites to value it for you. And put it up for sale, there is no commitment, you can even leave it on vehicle til someone buys it. I've used plates4less a few times. Been perfect transactions.
Years ago I bought T7 ALS cos it was cheap on ebay. Never knew we would ever have T7s.
I did approach Tails.com if they were interested recently but no reply. So it's still on my caddy.
I recently bought a T6. Absolutely delighted with it. And found T6 ALS for sale, Needless to say its now on the new bus.
I've bought a few and never lost on any, not a bad investment if you fancy a private plate.
My daughters cost £189, valued at 11k now , lot of luck involved I reckon. I of course I won't see that investment. Ha ha.
Good luck with your sale and a hope x y and z is okay and your health improves, that's the most important part.
Very best wishes, stay well
Ali