Wow! That's a big topic!
I would recommend that you try PPC for your start up site - sign up for an Adwords account and install Google's conversion tracking on your checkout.
Then trial a few simple keywords with some fairly strict daily budget restrictions. Make sure you're targeting the correct country - that's something many people forget.
Then monitor, tweak and monitor some more. Adwords will tell you how many clicks you're getting, what it costs, and how many orders those clicks have generated, so you can decide whether or not its costing in for you, and which keywords actually drive conversions.
Once you've done that, look at topics like keyword expansion, creative optimisation, landing page optimisation, landing page quality score etc, to reduce the cost per acquisition as you go along.