defaulted Private loans

I need help now. I am paying on Federal Student Loans and thought that when I started to pay that I had consolidated all my private and Federal loans together, but unfortunately I was mistaken and was out of the country for months and have defaulted on my Private Student Loans to the tune of $36,000.00. I am more then willing to pay, but the collection company is demanding $20,000.00 down and then they will arrange payments of the last amount owed with payments so high and with so much interst that I could not afford to live. I went to my parents for help and they are tapped out in this economy losing most of their 401K already. They helped me out with a small loan that I also owed which was part of this mess, but cannot do anymore. They are willing to help me with my Federal Loans so they don't default, and with my expenses I can only pay around $250.00 to $300.00 per month. I called some counseling agencies and debt relief help agencies and one company wants $1500.00 for their services and another wants $700.00, at least that is half? Is this normal procedure? and of course I cannot come up with $20,000.00 for the collection agency, so I am not going to find it easy for the $700.00 either. I am at wits end here, and I know this is my fault and I need to come up with something, but I need some input fast. Thank you for your time