Range Rover ownership is a lifestyle choice, they are unreliable, expensive to run and will empty a healthy bank balance quicker than anything else on earth.
But they are awesome machines to own, and ownership is not for everyone....
Cost is down to what is wrong...simple HGF could be a few hundred at a garage (couple of days work) but if it is slipped liners or a cracked block, then you may need to replace the engine block....a top hatted block from the likes of Turner Engineering or RPi could be upwards of £2500 to purchase, and then it has to be fitted...so you could budget £3kfor that....
Get two inspections done at two seperate garages....two you trust.....as most garages see a P38 come along and they see this as an opportunity to wrench the feck outta you for unneeded work.
Don't just take a single (and the first) garages word for it....
Often times, HGF can cause rock hard hoses, oily water, mayonnaise like oil, lumpy running, lack of power, water loss, low cylinder compression etc....
Slipped liners can cause similar symptoms and may even be heard as a metallic ticking noise as the liner moves up and down with the piston....only a strip down and inspection can properly diagnose a slipped liner or cracked block...
Best of luck and let us know how you get on.