2007 BMW 750Li Should I buy?

Hi there,
I've become aware of a BMW 7 series 2007 which a friend of mine is selling for parts. He's selling it for 500 pound or 650 US approx. The motor needs a complete refit and it needs to have a lot of general maintenance. Also it's a petrol which, I've been told, will mean it's worth less considering the price of petrol going up. My basic question was what sort of money would I be looking at to get it running well and would it be worth it to buy it to resell.
Cheers guys