The OP already has a HH5 i suspect he wanted to try and get a new one for free as you would,but was gobsmacked at their ludicrous charge for it.
I wouldn't want the first one, let alone want another one for no reason.
Look at it in the context that PN are offering a customer who is already in contract a product that retails for £106.23 + P&P for £99 +P&P as an optional upgrade mid way through his contract. Lets use the same analogy with Sky for example, try telling them you want to buy a 2TB box mid contract and see what they want for it - it'll be RRP and not the discounted new customer rate, same with mobile providers, this is how the overwhelming majority of industries that front the cost for your hardware to use the service operate. BT may own PN, but they can't just offer them cheap hubs in the same way that OR can't bung BT cheap wholesale deals.