How much of this debt do I need to pay?

I am trying to get my debt snowball rolling, which means getting a handle on how much I really owe. On my credit report, I have four different debts from one collection agency ranging from $900 to $50. They are old, about 4 years old (racked up from getting west nile virus and being uninsured). My question is this: The collections agency says I owe more than what I owe on my credit report (pulled from Creditkarma.com). For example, one of the debts is reported at $51 on my credit report, but the collections agency says it's at $286. I know they're trying to maximize their profit off of my debt but I don't want to overpay due to my own ignorance. I am aware that I can negotiate the settlement down, and to get that settlement in writing. Can I tell them I know the debt is at $51 and offer to pay that? What would be the smartest move? I am in Illinois and am mostly up on the debt collection laws here.

Any help would be great. I am a Dave Ramsey newbie and looking for all the not-too-harsh advice I can get.