I didn't pay 15k, I don't have that kind of money. I bought mine at the Reynard liquidation. Its not a seat, its a composite tub that has the shape of a seat and is built in a autoclave. Thats where the expense comes from, not too many composite shops have a big autoclave. It is very similar to the tub in the Ohio State stream liner.
Unfortunately everything in racing is gotten out of hand. when we were racing Trans-Am in the stone age an engine was about 25K-30K, now from the same builder a NASCAR engine is about 75K today. A liberty trans, that a lot of guys on the salt are running 8K new used about 6K. Maybe the pricing will reflect the economics of the day soon.
As for motorcycle those guys and gals are just plane crazy!