Yeah, ivrsell is spot on, getting all you ducks lined up is pretty important, and the first ducks in the line should be your stock platform. Once you have your products sourced, then you can consider setting up a selling platform.
Regarding an e-commerce format, take a good look at a Zen cart option first. Plenty of free options to go with or lots of skinning options if you want to style it.
This is one of my sites Link hidden: Login to view
it's a skinned Zen Cart. This site cost me $200, plus a few hours setting it up ready to stock. It's hosted on a cost effective plan from go daddy.
You really don't need to spend serious money on a site to get a good one anymore, and you can put your cash to better uses......driving traffic for one!