Well BMW have announced the end of i8 production in April 2020, so that could be one reason. Also they were made in relatively small numbers, so part that and being BMW, parts are going to be pricy. Smart looking car but there’s more efficient full electric and hybrids around now. It’s got a drag-co of .26 and from its 9.4kWh pack, it manages a mere 15mi on battery on average, (30mi on an exceptional day. And then it’s got a 1.5L under the bonnet. (The first ones produced, a 7.1kWh pack with a 1L under the bonnet.)
It could be a future classic but for now, it’s looking old in a future world. Even new ones are pricing at £114,000 from dealers. After April and the downturn in sales due to Cv, they’ll be paying customers to remove them from display. I’m not you; but I’d be inclined to wait a few months, then make a bargain basement offer. Or buy a Tesla Model Y LR tomorrow for £20k less or a Model S 100 D for £3k more.