British gas currently have a subscription method of getting Hive Active Heating for £9.00 a month. After looking at their terms, you can cancel the subscription after installing for a £150 fee, making the total cost £159 including the first month of the subscription service.
This is the cheapest I have seen for the installation version.
When you cancel, you lose the, hive Live, but still works as per the shop bought Hive systems.
Edited to add that this is only for British Gas customers, but from what I can see, you can take out Home care at the same time, for £10 for the first month, bringing the total cost for non British Gas customers to £169 installed.