Affiliate Marketing Secrets

I have been a member of a niche group website for much of the eight years it has been around. At one time, this website was thriving with new members, an active forum and constant interaction from the developer. However, along the way the developer has put less and less time into the site and the traffic has decreased by over 90% in the last year and held steady at 300-400 unique visitors per month.
The core group that is still around the site has complained about the lack of leadership and how the site is dying. I was not sure how bad of shape the site was in until I did some research, but I e-mailed the developer/owner and asked if he would be willing to sell.
He said, “of course” and I asked him what it would take to take the site off his hands since he no longer has the time to invest in it. He said I would have to make him and offer and went on to say that the site maintenance was “very cheap” and that with his ad contracts was taking in about $200-$250 per month in revenue.
Since I had no idea how to value a website, I begin to search on Google. I found several website value calculators that would provide values based on a number of factors. Most of the website value calculators I used (I used 7-8) gave me a value between ($290-600). There was one that valued it at $13 and one at $2400 but the majority were in the $300-600 range.
So, I responded to him saying that I had no idea what a website was worth and that based off of these site calculators and their guesstimates that the site was actually bringing in only $6-60 per month in advertising, I offered him $350.
I have not heard back from him in two days after getting almost immediate response the first couple of days. I know this has been him M.O. around the site at times, but I figured he would at least offer up some dialogue, especially since I found out his e-mails go directly to his iPhone (not like he has to log in to check them).
I wondered if maybe I insulted him with my offer? I know that if I were to hire a firm to build a website similar to the one he has, it would likely cost me about $2,000-3,000. On the other hand, he is putting very little effort into the site and many within the site’s community feel the site is dead or soon will be.
So, my question is this…how should I proceed from here?
Part of me wants to keep the website going just because it has meant so much to me and the other members of the community for the past eight years. There is another part of me that thinks with some effort, maybe it could be resurrected and possibly reach a level where it is bringing in $300-400 per month in revenue. Then there is the ambitious part that wants to build off of the site and grow it into something that could generate thousands per month in revenue.
So how should I proceed? Given his lack of time and commitment to the project, should I continue to press him to give it up? Was my offer too low and should I submit a revision? Can I do that without creating an atmosphere where I’m competing against myself? Should I notify some of the other community members of my intention and try to get them to lobby on my behalf or could I possibly create competition for myself where there is none if someone else were to try and take it over?
This is all new to me. The site has the basic structure that I need and that I can expand from and seems like it would be a much better deal than building a custom site. On the other hand, I cannot force him to sell and he may be content to leave it be and tinker when he can and just ignore the pleas of his community.
Any advice?
Thanks in advance!