Yahoo is not free. Actually there are not such directories. There are some pr6, pr5 well known free directories, like exactseek, but will not give you the same SEO results as dmoz and yahoo.
There are a lot of good directories out there. They're hard to find because of all the crap, but if you take some time you can find them. I'd start with directories in your niche. Then after you've looked at those lists I'd start checking out some of the high PR and high Alexa directories. Try to see if their traffic comes from the search engines. If it does, then you have a "good" directory that is going to pass on serious link juice...and even a few hits now and then.
Getting in PR 0 directories isn't always bad. If the directory becomes larger, the link begins to add more juice over time. You just have to hope the new directory lasts, so I wouldn't recommend paying for it. It's better to use a free option until the 0 gets bigger.
I think the most you can get the free directory is Dmoz, google likes it and for yahoo directory, you must pay annual fee which is so costly..