Some of the areas you are competing in are low margin, meaning the profit level is low so you have to sell a lot to earn decent amounts. This is true whether you are an affiliate, a drop shipper or selling the products directly from your warehouse. This is important because you will have to invest money in order to compete. At a certain point the investment to compete may outstrip any profit realized if you do not first have a carefully researched plan. Investment includes the cost of PPC, advertising etc., etc.
The costs associated with web hosting and acquiring/developing a website are relatively cheap, the barriers to entry are low. The barrier to entry for competing with established sites is high
. It can be expensive to compete, especially if you do not have a plan in place prior to embarking on your venture.
Before starting an Internet venture you must study who your competition is and have a plan on how to differentiate yourself to compete against them. You absolutely must have a link development plan in hand before a single line of code is uploaded to a test server.
Please be aware that a new site needs time to acquire links and more time for those links to be picked up by the search engines and more time afterward for those links to be fully utilized by the algo for ranking purposes. Furthermore there is no guarantee that the acquired links will useful for ranking.
None of the above is related to link development but I thought I would mention it because it appears you are trying to do more than your experience and financial resources will allow. What you need to do is step back and learn about how to plan an online business venture. There are numerous library threads (every forum has a library, the link is below the ittle of the forum) that contain many of the best discussions.
Before you move to link dev I would suggest you start at maybe square two and check out the new to web, webmaster business, and ecommerce discussions archived in the library. I did a summary of some key discussions here
[webmasterworld.com], please take a look at those.