The 1TB version is also available for $296.65
Yes it is overpriced compared to a bare Gen 4 NVME SSD and hopefully MS reduce the RRP soon but if you want the official expansion card this is pretty much it right now.
Alternatively you can get a CFexpress adapter and look for a suitable 2230 sized card but consumer availability of larger sized variants is currently limited.
Gen 4 NVME SSD, will this work in a PS5? ;p