Registered less than a year ago, domain hack Li.st sold for $35,000 at DAN. Checking out Tian.hu for whois as they give data on premium registrations and renewals they show the reg fee at premium and $494. This is the highest reported .st domain name sale of all time. To be fair there are not many, less than 50 all time.
Checking out the .st registry they say, Domain registration and renewal price is 29 EUR per year. There is additional domain registration fee for 1 and 2 letter domains.
