set up a Yahoo advertiser account, add keywords terms to your campaign like you are going to advertise under them but keep it "paused" then goto the keyword bid option after selecting all of them and you can scroll down the list and see the highest bid on that term..then you can look up the terms in yahoo.com and see which advertiser comes up first and guesstimate everything from there..but keep in mind the advertiser with the highest bid may not be on top because their new system will put the company with the most clicks and dollars spent advertising ahead of other lesser ones..so the $10/click may actually be the third one down and the top one may be a $7/click...just a fyi
Hope this helps!
(you can always send me a few keywords and I'll check them out for ya!)
Chris