As far I know Atheists don't believe in anything that has to do with religion and a soul is part of that.

Some do, and some don't. It's a philosophical as well as religious topic, and it's not a consistent belief among atheists as far as I know. I go back and forth on it. I certainly don't believe in a soul in the traditional sense, of something that floats around in the ether and enters the body at conception and leaves at death, to heaven or to the next life or nirvana or whatever. The closest I have to that concept is the individual consciousness, something that humans have that most other forms of life don't. Perhaps some higher animals do, but not to our degree. We have self-consciousness, we have an "I", we have awareness of our existence and of our eventual death that I don't think even the smartest dog would (although that's certainly up for debate!). But consciousness is somewhat mysterious - where is it located? How is it generated? Why do we have it, when other creatures don't? If it's a strictly physical property, why can't we create consciousness in an artificial being? Can an individual consciousness be preserved beyond the death of a body, downloaded somehow, or is it irretrievably tied to the physical body that developed it? I suppose this is like a soul. But I feel that we are tied to our physical bodies, to the chemical composition and electrical firings of the brain and the sensory input we get along the way.. and I don't think such a thing would survive the death of the body. The idea of the soul as I've heard it seems to go beyond the physical and imply an afterlife of some sort, so it's not really the same thing.

Atheists don't necessarily have any beliefs in common with each other. Their only guaranteed commonality is their lack of belief in deities. Any other commonalities are incidental. I would guess that you're mistakenly conflating "materialist" with "atheist". Certainly, many American atheists also happen to be materialists, but there is actually nothing essential to atheism itself that precludes one from believing in a non-material component to reality, of which souls might be a part.

i'm not an atheist, but i'm agnostic... why, how much would you give me for my soul?

There is no "atheist" set of beliefs that covers everyone who says they are atheist, so there would be different views. Some might say the soul is the emotions or the rational part of the human brain( the part that thinks), some might deny the idea of a soul at all. It is interesting to contemplate however, that Buddhism, in its original form, was at best agnostic, at most, atheistic, yet still, there is a concept of a part of a human that continues after death.

I can speak only for myself but I have to say that I can't believe in anything I can't define. What is the definition you use and we can start there. Interesting question +4

You have the question back-to-front. As an atheist, I only believe in things for which I have a defintion, and some evidence for that defintion. "Soul" is a religious concept; to an atheist, what you are saying is "do you belief in frugwuz, and what is the definition you would use?". I have no idea what a soul actually is on order to believe in it; where is it, what does it weigh, how does it affect the behaviour of what?

I don't. But I'm aware that some do (in a spiritual sense and/or poetic sense)