slightly eye watering £12,400 with only 5 properties passed
There's a good chance that your final bill would be less than that, maybe even half
. But you'll have to pay £250+VAT to find out.
If you run a business, you may be eligible for £2,500 DCMA gigabit voucher.
I just can't understand how there are only 5 properties passed
"Properties passed" means "properties where service is available to order" - not the properties which the fibre cable goes past on its way to your property. The fibre cable can't be cut to provide service to other people.
That is, they will put in a fibre Connectorised Block Terminal (CBT) to serve you, and there are five properties altogether which can be served from that point. They'll also have WBC FTTP available (at no charge) once your FTTPoD order is fulfilled.
You could try to club together with one or two of them to share the cost, but note that the actual set of properties passed won't be finalised until the survey is complete, so it may change.