Dan.......i am assuming you are not US based?
But more importantly you can list either through Small Business Listings on which there is a 15c per click cost with a trackable ROI through their newly introduced tracking platform for small business.
f you list with LOOK and your site is accepted you will appear on ALL the LOOK partner sites of which the most important is MSN.
Secondly you can choose Large Business Listings but this requires a minimum monthly spend of $2500 and is more suited for the larger clients such as IBM,Fed Ex etc.......where the click rate is negotiated on a deal by deal basis.
Thirdly you can list geo specifically through LOOK Australia and or LOOK UK.
However in both htese locations there is NO cost per click for small business listings........there is a annual listing fee.....however if you choose to list as a large business listing in Australia you will then be listed on Yahoo Australia and New Zealand but again this is charged on a per click basis similar to the US model.
The UK has NO per click rate and nor will Japan when it comes on line at this stage.
On tracking..........LOOK recently introduced its Tracking "Primary Knowledge" platform to ALL of its small business listings along with some other importnat changes.
Such as multiple URL's for the one set up fee.....reduction in the cost of making changes or updates to listings however changes mae within 30 days are free.
I personally would NOT use OVER or Google.
OVER recently signed a deal with Gator and has raised its minimum bid price and there is quite some strong talk OVER is at some risk of losing Yahoo.
Plus of course OVER is an auction based model where there is NO certainty on cost per click and needs constant monitoring.
LOOK on the other hand allows you to set a budget spend and you can top this up if the results warrant such top up or you can simply leave your ad spend and get NO more referrals until the next accounting month.
Hope this helps and perhaps provides you with the answers you require.