You can make 159 valid words from the letters in COSTARS using the Scrabble US/CAN dictionary.
How many points is COSTARS worth in Scrabble?
COSTARS is worth 9 points in Scrabble (US/CAN) and 10 points in Words With Friends.
How do I use the Word Unscrambler tool?
Enter any letters into the input box and press Search. The tool will return every valid English word that can be made from those letters using the dictionary you select.