You're from the UK. My bet is that you can find better nebari and better branching for about 5 quid and half an hour of digging if you drive for about 40 minutes and ring some doorbells.
You guys use as much beeches as we do for gardens, probably even more.
Not trying to be a negative nancy here, but this tree needs a lot of work. 90cm is tallllll.
So if the whole apex needs to go, and you'll have to spend 5-8 years rebuilding it, and the pot is worth about five pounds.. And the nebari isn't something awesome.. 50 pounds is a lot of money.
All those things considered, I would pass up on the opportunity and just post a message in the local paper or marketplace asking for stuff you can dig up.
Air layering beeches and hornbeams can be difficult.
But if it speaks to you, and you think it's worth your money then absolutely go for it!