Why not? You need more links to get better ranking in the search engines right?

Yes, you do. But stop drooling for a minute and think about it: that many links for that little money always means the links are spread across just a few domains. The search engines will only count one, count 'em, one link from each domain as a rule. The others are basically ignored or so completely devalued as to be almost worthless.

That just makes sense. If I have a domain with a thousand pages on it and I put a link in my footer across all of my pages to some other site, does that really make that target site "popular"? Common sense says no. It was just easier for me to add it to my footer.

So beware of the advertisements for thousands of one-way links for pennies a link. Unless the sites can prove that they get a lot of traffic, and it's the kind of traffic that will click on your link and visit your site, it's not worth it.

For the right way to build link popularity and get traffic both from the links and the search engine rankings those links give you, I recommend Jack Humphrey's Power Linking methods.