How much sinew would it approximatly take to back an average length horn bow?  I know its a vague question and what not, but I suppose I'm looking for a vague answer 

.  To narrow it down I guess say between 45 and 55 inches in length.  Any other info you feel necessary is also welcome.  Figured I'd ask the questions before I did any damage to my bank account and/or pride.
Thanks and have a good one.