my car wont start, the sterring lock is stuck, key wont turn in the inginition, nothing will work.

i went to get into my car after picking my kids up from school and the key wouldnt turn, i pulled on the wheel as the sterring lock was on but the key still wouldnt turn. i had to call out my breakdown company and they said that its the sterring barrell that has gone wrong. do you know off top of your heads why this has happened and how much it will cost to repair??