Marc Lore, the Bucknell grad who cofounded and sold it to for $500 million in 2010, has raised $80+ million more (from VCs Accel, Bain, NEA, Western) to start Jet, the Montclair, NJ-based "shopping club" he says will challenge Amazon Prime from a Hoboken headquarters (corrected) which will open later this year.

Jet also plans to operate "fulfillment center" warehouses near Swedesboro, Gloucester County, and Reno, Nevada. Business model: For $50 a year, Jet members are guaranteed the cheapest prices on the Web.

Other Amazon competitors include eBay Enterprise, the King of Prussia-based successor to Michael Rubin's GSI, which has been cutting employees and preparing for a sale or spin-off; Rubin's successor business group, Kynetic, which is partly backed by eBay's China-based competitor, Alibaba; and a collection of niche and specialized digital retail outlets.

Can Jet deliver for shoppers and investors? "We find Jet very interesting. The valuation proposition is variable," Tom Caporaso, CEO at Clarus Marketing Group, Conn.-backed operator of the discount service that competes with Amazon Prime, told me. "(Lore) is saying they can deliver prices 5 to 6 percent lower than anywhere. I don't know how he will do that and still make money. He's trying to out-Amazon Amazon."

Jet has attractive features: "Their membership fee, at $50, is half that of Amazon Prime. (Lore) has raised $80 million based on his credibility from The Wall Street Journal, TheHub and the (financial press) are driving publicity."

But, Caporaso adds, Amazon has long shown it's willing to sacrifice short-term profit for market dominance. And looking back to the negotiations, "there was a lot (Amazon boss Jeff) Bezos did to get the price he wanted," recalls Caporaso. "He dropped the price of diapers 30 pct. If he wants to Bezos could easily lower the price below Jet."

So it will be interesting to see on what basis Jet competes: "Does he take this Costco-like model and try to drive bulk purchases more than single-item purchases? That's Amazon's wheelhouse, the Subscribe and Save program. He's going right for the head of the beast."

Clarus and its sites serve clients through FedEx; the 15-year-old company employs just 150, two-thirds of them in customer service. "We partner with the companies to do all the transactions; we push customers their way; the pitch is to the consumer, to save them money," Caporaso told me. "Very much like (Kynetic's) ShopRunner. Only ShopRunner aggregates 80 (large) stores. We have 1,200-1,500 stores. We offer free shipping plus returns. They are an annual membership; we offer month to month. We work with everyone you've heard of: Walmart, BestBuy, Victoria's Secret, Kohls, Sears. ShopRunner is more like Michael Kors, a bit higher-end. Amazon is the everything store."

Founder Vin Villano worked initially from his Middletown, Conn. garage. Clarus was for a decade a cash business; in 2010 Norwest Capital bought in.