In an effort to boost its ecommerce and interactive marketing capabilities, eBay has agreed to acquire GSI Commerce for $29.25 a share, or total consideration of approximately $2.4 billion. The acquisition, which will be financed with cash and debt, is expected to close in the third quarter of 2011.

According to a press release from eBay, the merger consideration represents a 51 percent premium over GSI’s March 25, 2011, closing price and a 47 percent premium over the average closing price of GSI Commerce common stock over the 30 trading days prior to March 28, 2011.

“We intend to lead the next generation of commerce innovation. The acquisition of GSI, which offers the most comprehensive integrated suite of online commerce and interactive marketing services available, will significantly strengthen our ability to connect buyers and sellers worldwide,” said John Donahoe, eBay president and CEO, in a statement. “Combined with eBay Marketplaces and PayPal, we believe GSI will enhance our position as the leading strategic global commerce partner of choice for retailers and brands of all sizes.”

Earlier this month, eBay made it free for users to list up to 50 items per month in auctions at any start price, and free to add the “Buy it Now” option to those listings, to appeal to auction enthusiasts as well as shoppers who want an immediate purchase. Effective April 19, 2011, the new pricing builds on a series of free-listing promotions in 2010 that drove significant increases in both new listers and listings.