1) £7 bln was only the rate if you don't evict the 650 incumbent morons that use it as office space. Remove them it becomes cheaper.
2) You don't have to cover it all in one go. Get a cheap loan from the lottery fund and pay it off with tourist income over a few decades. For example, the Second...
If the pigheadedness of MPs is going to double the costs, then taxpayers should cover the cheapest price, and MPs should fund the difference out of their own pockets. That'll learn them (although it probably won't).
Alternatively, I agree with those above who say move parliament elsewhere to...