Blue Duck I think was the first one to sell his - or one of the first, and I believe he sold it to HSX for around $900...there were even a few newspaper stories about this "HSX" movie site where people could trade movie stocks, and then SELL their ports for REAL cash.. It was quite the story back then...
You would find these purchase ports on the LTD board as "HSX Bank" purchases. After that players continued to sell ports to HSX. As time went on (SADLY) they quit buying these ports for cash (RIGHT before my port hit $200M!!).
After that, some players started selling their ports on eBay...some were sold for quite a bit of REAL money...ports over $1B even, and these 'new' players shot up the LTD Boards without even having to "pay their dues." Some of the long term players resented these players for shooting 'past' them without even "earning" their rank - but buying it.
Today, you may still find ports selling on eBay, but I doubt a port of $176M (while a well earned size) will net you much money - but I may be wrong, I just haven't checked to see what ports sell for there any more...
Good luck though.