I don't think its worth $300. If you're looking to build PR, you can do it for less $. If you're loking for traffic, Yahoo is the wrong place. Most people use Google.
Well, I haven't acquired a yahoo dir link for quite some time so can't say whether a link would pass the kind of value it used to. It's a tough one. If you have the budget and you won't miss $300 then go for it. You won't get any click throughs but should get a bump in the SERPs especially on Yahoo. If you don't really have it, spend that $300 on something else. Do some research, create a great article or blog post and promote it. Or why not create something like an infographic and promote that via blogs and social media?
IMHO not even worth it! I list on yahoo and google in 2 weeks tops with simple blog sites, now maybe if you are looking to get ranked super fast, but there are other ways to give google and yahoo the things they want.
There may be two reasons for choosing Yahoo Directory. One is for getting PR and another is for Visitor. If you're planning to get visitors or sale by using Yahoo paid directory service, it might not be help you so much. first of all, we require the statistic of the visitors that yahoo is getting at his directory section. and if you're trying to get PR, then it's may be help you. Google gives priority to Yahoo Directory, Dmoz and some other high ranked Open Directories. so, i think, that'll surely help you to get PR.
I think it's worth it. It's an expense thats many spammers can't afford/won't pay and many serious businesses invest in - in good faith. Because it's such a loud SEO tactic the value isn't what it used to be but it's still valuable. Every little bit helps - if your competitors have a Yahoo! directory link then you need to have one, if they don't then that will set you apart.
Definetly NOT worth 300$. Using 300$ with isnare.com+dailyarticle.com+keyword research+targeted keywords in anchor texts would give you a LOT more SERP Power! Speaking of experience ;-)