Does anyone have any tips on how to start with Collection Agencies?

I have about 6k in debt over 5 different accounts I'd like to work out, but i'm not having any luck with collection agencies. They all want high upfront payments (ie $600 per month) which just isn't in my budget. All these debts are about two years old, so I don't know that validation of debts is an option any more. Beyond that though I'm not disputing the debts, but I just want to have a starting point to go from that I know I can stick with. I've told them I only want to deal in writing and no payments over the phone, and they give me a hard time about that. It's all very frustrating, considering it's something I'm not trying to avoid. Any advice would be very welcomed.