Hi guys!
My name is Serg and I'm from Russia 
Very glad to be here!
Thats my problem:
I have a friend who is very skillfull in SEO.He is collected a double optin list of about 41k subscribers using SE traffic and awber as an autoresponder.As I know he is never tried to monetise this list.
Now he is offering me a full access to this list cause he have no time to work with it.
He told me if i make him a good offer he can sell this list to me but I have no idea how much $ it can worth.
Any ideas?
Subscribers in this list are dating related.
I am not sure how close you and your friend are and what level of trust exists between the two of you, but I will say this: Buying the list outright is a risky proposition.
As I see it, you have two main options here.
1) One is to buy the list outright, as you said.
Unfortunately, is is damn near impossible to pinpoint what such a list would be worth without understanding the funnel used to collect those leads. I don't think they opted in for nothing; where they signing up for a newsletter? Registering to get a freebie ebook of tips? It isn't always possible to know the answers to these questions, but in your case it seems like it would be easy to just ask your friend, so these are the first questions I would find out the answers to.
A list that's been incentivized ("FREE ebook chock full of dating tips!") and then let down (with a shitty ebook) is far less likely to be responsive to further monetization than a list that's been cultivated carefully over time. Furthermore, while a list that's been carefully cultivated over time will be worth more than a forlorn one, it's worth making sure that any offers you mail out to the list match the "voice" that the subscribers are used to hearing from the listowner. Sure, you can make money just mailing shit out, but you can make a lot more if you don't suddenly bombard the list with random offers that have nothing to do with the material they've previously received from the listowner.
If you choose to go this route, offer a test buy. Say you'll email out a random sampling of 1000 list members, and agree to pay a flat fee for this privilege. Don't worry too much about what you you pay; with such a small sample, you're bound to not be out by much, even if the buy bombs spectacularly. I wouldn't pay more than LOW two figures for the privilege of mailing out 1000 members, but, hey, I'm cheap. 
Once you have better data, then you can consider purchasing more of the list.
Be careful! Lists collected through SEO efforts are typically collected very slowly; that means some members of the list will be newly registered to it (say, a few days old) and some will have been on the list for ages (years, perhaps). Older members are FAR less responsive, so you need to make sure that your 1000 member test buy is RANDOMLY sampled from the list if you want to get a sense for what the full list is worth; otherwise, your friend is likely to just hand you the 1000 most recent subscribers.
2) The second option is to do a revenue share. Offer, for example, to share 50% of your revenue with your friend. Personally, if you trust your friend and he trusts you, I'd just go with this option. It aligns your incentives much better than just buying the list outright.
rev share FTW.....def the way to go.....
I'll go with the opposite of polar, I hate revshare and would want to buy it if possible for as cheap of a record as possible. 
I always prefer 100% whenever possible, even if that requires a lot more upfront investment.