Marc Lore does not remain still. During a recent lunch he fidgeted in his chair, stood up, stretched, then took a seat, and resumed eating. "We have an open office. I stand all day, I never sit," he explains. "This feels uncomfortable."

Lore has been very busy of late building Jet, an ambitious e-commerce startup trying to take the shopping club model pioneered by Costco and reimagine it for an online world. Today the company is launching in private beta to its first 10,000 customers, a slice of the 360,000 people who signed up for early access. The goal is to offer better prices than even the largest web retailer, Amazon. That's an ambitious battle to fight, and for Lore, it's also personal.

Lore built his prior company, Quidsi, into a leading online retailer across verticals like Diapers.com and Soap.com. In response, Amazon initiated a price war, cutting prices to the point where it was taking a loss on every box of diapers it sold. When the buyout offer came, Lore's investors encouraged him to surrender. He accepted a $545 million acquisition and spent two years working for Jeff Bezos. I ask him if he felt like the sale was something he wanted, or something he did under duress. "A little bit of both," he says with a wry grimace.