What is the Value of A 1950 D $20 Dollar bill with a Star on it?

Answer 1

When you say Star, I assume that the star is at the end of the serial number, correct?
That makes it 'better' as a collectible than a normal note. Circulated normal notes in lower grade don't sell for much over face value, but a Star note in better grade might be pretty good.

Here is a listing of all Series 1950 D $20 bills presently for sale on eBay. One of them (as of 23 January 2007) is actually a star note but has six days left to run:
http://coins.search.ebay.com/1950-d-20_Small-Size-Notes_W0QQcatrefZC6QQfgtpZQQfromZR2QQfsooZ2QQfsopZ2QQftrtZ1QQftrvZ1QQlopgZQQsacatZ40028QQsaprchiZQQsaprcloZQQsatitleZ1950Q20dQ20Q2420QQsbrftogZ1QQsofocusZbs

Answer 2

You can take the help of Ebay auction... and let the bidder decide on the real value