I was doing a search and although I know this would have been asked in the past, the pages I looked thru didnt give any usefull info so i will ask here....

I know each plane, or qty of the order will vary, but on average how much of a discount would an airline get buying new planes? I am not really talking $$ just a percentage such as 20%, 30%, 50% off list? I have always been curious about this. One reason I was always curious was the price of the CRJ900 and the 717-200. Thank's for any help.