Setting up a text link campaign which is tracked would be no different from a graphical ad campaign.
If your charging/invoicing based on clicks you do really need to understand the volume of your traffic and estimate realistically what you can deliver if your selling it.
Not much point selling on a click through basis if your not 100% clear on your site traffic and click through levels, and what you can realistically deliver.
I dont mean to sound pessimistic as I dont know what your doing, just a word of caution.