A nice-looking auction site is a breeze. Mine cost a couple of grand and most of that was in the visual design -- it runs on PHPproBid like many other small auction sites do.
Getting traffic and listings is a whole different ball game. 'General auction' sites like Moneyca simply do not stand a chance of competing against eBay. Think about it -- huge companies with deep pockets and major motivation have gone up against eBay and universally flamed out (Overstock and Amazon are the two that come to mind.) Small sites catering to niches that eBay either prohibits or tightly restricts, or which otherwise take advantage of the little chinks in eBay's armor, are the only ones that really stand much of a chance of getting off the ground.