If you're site is non-commercial (no ads, memberships, donations, etc) you can submit for free - otherwise you must pay a $299 review fee ($299 per year) - and this does not guarantee a listing.
The Yahoo directory link can help with your web rankings oin both Google ad Yahoo search engines. For simply seeing your website indexed in Yahoo you do not need that link because gradually your site pages will be visible in the Yahoo engine.
Doesn't $300 a year seem a little much if you're not guaranteed a listing? Yahoo is probably making a killing.