Pretty sure it's $100 USD isn't it? https://www.theverge.com/2020/9/3/21419025/mario-kart-live-home-circuit-nintendo-switch-ar-remote-control
That's for the basic kit. I think what he means is the price to get a second kart as well (or third, fourth - IF it supports that many. Pretty sure only 2 players - particularly based on that presentation - but IIRC they haven't made that officially clear yet...).