With respect, I know how much these seats etc cost from audi, yes eBay etc it's above the prices but in reality, this is well below the cost to buy them from audi, they're ridiculously expensive to buy new, it's an 8Y, speculate to accumulate.
I work with seats & parts often, these things are serious money.
Seat covers of this nature are sometimes £500 each & that's not for the whole seat cover set, it's just 1 piece as in base or backrest etc.
Covers can be 1k plus per seat let alone anything else.
4k may seem expensive but it's not if you look at new as in buying parts from audi not speccing for a new car.