Anyone have experience settling with debt collectors?

Hey all. I'm coming out of a rough financial patch of my life. The last year I've lived on very minimal income, and spent most of it without health insurance despite the fact that I was diagnosed with a rather expensive disease roughly the same time all this happened. I think I've managed it fairly well, but it was inevitable for me to incur some debt. Now all of those bills have been turned over to collections.

I'm finally on the upswing, and I'd like to start settling this to get some peace of mind. I'm not sure of the exact amount I owe since it's several bills, but it's probably in the neighborhood of $500. Could be worse I guess, but it's not exactly chump change.

Anyways, has anyone here been in a similar situation? I've heard stories of collections agencies settling for reduced amounts in order to get anything at all. I've got one of the bills in front of me right now, it's $158. If I were to call and say something along the lines of, "I have an extra $100 from my check, it's yours right now if we call it even", do you think I'd have much success? Should I go even more aggressive on the amount?