It’s simple, how much is a brand new bare tank in primer from BMW? Probably around £1500 plus 20% VAT, (£1800) and that’s if they are still available, then get a top quality paint job, add a filla cap, add two petrol taps, add two BMW badges, add a pair of knee pads, then add the decals, including the Gaston Rahier decal and you are are into a lot of dosh, certainly northwards towards £3k or more.
Regarding tanks made in India, the ones that I have had experience are absolute sh#te!
Would you spend what it costs to do a top restoration on a G/S and then put a fake tank on it, I doubt it.
Still a hell of a lot of dosh though!