It would depend on the type of site you run.
Some sites are a work of passion with little monetization of traffic. They're essential and important to the general well being of the internet.
For these sites, I'm sure webmasters could fork up some $'s comparable to the cost of their hosting. Perhaps this is added to the hosting plan as a few dollars per month by the ISP. (Go McDonalds style with this one.. not Mortons'.)
Some sites are affiliate sites and while they monetize their traffic the ROI is not significant enough to justify trusted feeds, besides, do trusted feeds handle affiliate sites?
Again, I suspect webmasters would pay $'s which are a percentage of their earnings, pennies on the click? Figure out a way to get into the affiliate cut without taking the affiliates out. Keep in mind that many of the affiliates (perhaps a majority?) are hard working put their hearts and souls into their work.
Figure out a flat fee type deal for these folks. $150 per month per site. The site gets a review every quarter and the $150 pays for the bandwidth of the spider and the chunk of HTML spewed out in the serp.
Ecommerce sites would again have to pay comparable to their profits (not sales, mind you) on the click.
Now here's the fun part.. we run all three types of sites, they're essential to our diversification and our survival. Unfortunately, our audience is based in a small part in Asia, who, while they search the US engines for their widgets do not justify spending the huge $'s per page that is currently offered by the various PFI players.
Today we have to deal with a plethora of regional 'hoos and 'tomis and 'oogles which makes it extremely difficult to justify the spend online. We're better of doing PFI in dead-tree media for now. ;)
Add some geotargetting to the PFI and CPC type deals while you're at it -- i.e. if someone from Elbonia searches for black widgets a store selling black widgets in elbonia comes up number 1.
We're getting there slowly... its close, but its no cigar.