If you mean to buy to transfer into your name, all I can tell you is my personal experience: I won an auction for a fully-loaded 12K WM account on eBay in October of 2017 for $1556, out the door. Seller paid all costs, and the ongoing maintenance fees until closing. I'm told that was a steal of a deal, at about a third of the going rate. My recollection from what others have said, is 12K accounts should sell for about $4000. Others will have better numbers for you.
A lot of the value has to do with how many credits come with the account. Mine had 12K from the previous year, 12K for the current year, and 12K to borrow from the upcoming year. With Housekeeping tokens in place. A "stripped account" (with no credits in it) would/should sell for a lot less.
Just found this on another thread, quoting
@taterhed: "My rule of thumb is: < .40 cents a credit, fully loaded, all-in (transfer included). So, an account with 10k bank, 10k current and 10k to borrow (30k points) and 3 HKTS, $4000 dollars (including the $299 transfer fee)."
Hope this helps a bit.
Dave