They dont sell them.  It's bitcoin native names.  Anyone can make one.  If you use one of their wallets they might charge you a slightly higher fee.  But just make your own tx.  And you own that name forever, according to the spec.  We've been missing names on bitcon for ages.  They actually stumbled upon some innovation.  You format the OP_RETURN according to the spec, and you get to own the character string if you are first.  This is useful for a lot of things, including with nostr.