How much adsense pays for each click for a very low value keyword?

[Jake]

The publisher's cut is close to 50% of the advertisers click cost, you could get and Adwords account with the min. deposit just to secure access to the keyword tool that shows the estimated cost for various searches
You may find that your site gets a different makeup of ads, possibly a large percentage of remnant ads picked up by re-marketing services that seem to stalk users around the internet with ads that will have nothing to do with your page content.

At the other extreme, there does seem to be some sort of payout cap that prevents Adsense sites from earning huge money from doctor and lawyer terms who's cost has been bid into the stratosphere, these clicks some dream of getting may be only allowed on 'authority' sites.