Maybe $200, like was already said. But probably lower than that. A simple ranking fall could take away most of the site's traffic, so I would be a bit wary of paying too much.
Truly said above, pr drop can loose your scope to make money but you can earn the paid amount in 6 months as well. $200 is a justified bid for the site.
the way adsense dropping income these days, its kinda risky to buy a site with purly adsense revenue. the site might be making $30/m but what is the source of traffic? and is the traffic and revenue sustainable for the next year? make sure you analyze the traffic source and get proof of revenue. usually a site like that is valued at 10 x monthly profit, but as i said above, the way adsense revenue is dropping, i would agree with other sand say $200 is somewhat of a safe bet.
Check the quality of the backlinks, make sure that traffic doesn't depend on a PR7 link that might 'disappear' once you buy the site... 10 x the monthly revenue used to be the rule of thumb here, but these days not many sites get that much... You have to wonder why someone would be willing to sell a site that consistently makes money...
Do you mean Page Rank drop? C'mon guys i own a PR1 site that ranks top 2 for a special keyword and have a daily income of $45-$80 just from that site... and this has been like this for almost 2 years. EDIT: Content is king, not PR.
Fair enough you want to pay that much but I wouldn't, having said that I haven't seen the site or anything so it might be more or less.
well my formula is Income X 6 months = Your BIN! 30 X 6 = $180 plus all these count + if ur domain name is good + your content + number of visitors
$1 day x 30 days= $30 month x 10 = $300 So if you ask me IF i would pay for it i say No cause i dont need any more sites. But, if i wanted it very much, yes i would pay $300 for it, as long as all traffic is coming from serp's. I'm a pretty clever and pro active SEO, so i would take care of that site to get even more traffic. After all, it would be a good deal that i could pay off in 2 months. But i dont need more sites, just need to take care of existing ones. Content is king, Traffic from serp's is king. Trust me. EDIT: One of these days i'll write an Ebook about me!
You can't just look at the site revenue, and tell the price. The site contents, members, backlinks source... is what you should look for in the future.