Not to disappoint you, but you will hardly ever succeed. There is a reason why eBay has started charging so many fees, they're not as profitable as they used to be. What do you think it costs to run an infrastructure like eBay's? That's where a lot of the fees goes. Look at Craigslist, much simpler and much cheaper to run. Once you get into eBay territory, your costs are going to be huge, so you will start charging fees like they do as well :-)
Just lowering costs is not really a good way to start a business unless you bring in something else. You should rather find a niche and create an auction site for that niche with the tools they require.

my .02 cents