For
serious investment purposes?.... Yahoo Directory...
The Yahoo fee doesn’t guarantee insertion in the Yahoo directory. Payment gets someone from Yahoo!'s editorial staff to review your website, and to mull over your proposal to incorporate your website in their Yahoo directory, and to reply to you promptly. They will add or deny your website from the directory at this point.
If your website is denied inclusion in the Yahoo directory, you have the right to appeal and/or make changes to your website, (in a given timeframe), and you will be able to re-submit your website without paying an additional fee. If your website is accepted, you'll be charged the same annual fee the following year to keep your website in the Yahoo! directory.
Yahoo! has the Number 1 Alexa ranking. Yahoo gets more traffic than any other site on the Web. This is why you should have a Yahoo directory listing.
Being listed in Yahoo's elite, hand-picked directory is one of the top methods to ensure that Google's (Alexa rating = 5) crawls and picks up your website home page quickly. A link from Yahoo! will also improve your Google page rank. Eventually, Google will find your website, but if you want heaps of traffic quickly, a Yahoo! listing would be your best choice.
The other options in your list could still be done - web redesign,
SEO - reasonably cheaply - if you have a friend who can help you out with it.
Offline promotion - unless you have a shop/premises where people can come and see the goods - isn't usually that effective.
You may also want to start a
blog - linked to your website - that can also attract traffic.
I hope that helps a little in your decision making :)