All,
As you may remember from the thread I started back on Oct 20 about eliminating the minimum spending requirement for US advertiser sponsored search campaigns. Thought I'd alert the community here that we've taken one more step to making advertising with Yahoo! easier and more convenient - we lowered the minimum deposit from $30 to $5 for any US advertiser.
Basically, you can get started with a deposit of $5 and use it to pay for the click-through charges for your campaigns. After your initial deposit, you spend as much or as little as you like each month based on the keywords you select and how much you bid for each one.
You can check out the post about this on Yahoo's search blog:
http://www.ysearchblog.com/
YahooSarah