PPC vs SEO in Small Paid Niches:

The more expensive the associated PPC ads are the more value there is in
performing SEO on a site in a paid niche. If the average cost per click is $5 then a
$1,000 SEO campaign pays for itself after only a few hundred targeted visitors. YSM tends to be a bit sloppier than Google at monetizing niche advertisements.
YSM’s open bidding means that if there are only a couple strong advertisers one
gets to stick the other and then get their ads cheap.

I have one client that gets most of their Yahoo! clicks at about 12 cents when her
competitor pays about $8 a click. On Google I pay closer to $3 for each of those
clicks.

If you are unsure whether an SEO campaign would justify its fees you can run a
test PPC account to see what type of demand there is in your target market.