Do a search online on Road and Tracks website. They posted an article on it about 2-3 years ago when they did the first US test of the McLaren F1.
*Edit* I couldn't find it on their site, but if you go to the library or some place that has backlogs of Mags, it's in the Dec '97 issue. They talk about the conversion process, the reason why the seats have to be taken out, and the price.
Ohh, and the company is called Ameritech. And the conversion is mutliple $100k's looking at my current issue of R&T in the Road Test Summary.
They show the list price for the F1 at $890,000 with an as tested price of $1,131,120. So the conversion was $241,120!!!!!