I have Had first hand experience of Cipher's driveway, and indeed, I can confirm that I wouldn't want to drive my car over it on a regular basis!
What about your manifold Ben, didn't grounding the V6 on this awful bit of kerb crack that too? I wouldn't like to think what VX would charge to change that, because as you know, going by the book it's a head-off or engine-out job! (I've yet to try the "DTM" method of swinging the engine over...)
In terms of price, it's the Cats that will bump it up for you. As mark says, they're in the region of £300+ each.
My friends dad works in the parts department of vauxhall, (very handy guy to know) and it's only recently he's agreed to supply me with bits for my personal car at trade price. My new exhaust backbox on my V6, and both mid-sections, came to a total of £119.
Like the others say, if you can get the developers of the housing to pay for the damage, then go all out and get the full Vx system fitted!
Without meaning to sound at all rude, I seem to remember your V6 is the same year as my V6, (N), with simelar miles, so taking this into account, if you DO have to fork out for a new exhaust yourself, you may not benefit in the long run from buying genuine Vx, if you can get OEM/pattern parts for a much reduced cost, eg. eBay! I know GM parts are best, but equally it might not be in your best interests to spend more on an exhaust than the car is possibly valued at with the new exhaust fitted!
Either way, good luck with getting it sorted!
Cheers
James