It would appear I don't value it at £230 before I commence receiving a service.
To put that in context, BT quoted me £25,000 to install a 100Mb fibre

so £230 doesn't seem that excessive

SovG had to raise £12,500 to pay BT to install FTTC after Persimmon refused to allow Gigaclear to install fibre on the estate without a huge ex-gratia payment up front.
As I said before, you can install yourself saving £129.99 or find someone else who will trench in the fibre from your boundary into your house and install the router. It doesn't have to be Boxcom and it's not complicated - the £100 connection charge is, mainly, to cover the cost of the cable kit (Google 25m pre-terminated fibre and you'll see it's not cheap).
Personally, I don't see £129.99 as being excessive for a Boxcom team to come to Cliffe and do all the work for you.
On the flip side, with a lot of the village now using Gigaclear and SovG getting FTTC, the ADSL service (conventional broadband) isn't likely to degrade too quickly from additional use (congestion) so if you're content with your current ADSL service stick with it until you get to the point where you aren't.