The online market for travel services will reach $63 billion within a few years, and Priceline.com aims to capture a significant share; already, it is high on the top-ten list of travel Web sites. After a brief period of diversification into name-your-price sales of groceries and gasoline, the company has refocused on its core travel and financial services offerings, including airline tickets, hotel rooms, rental cars, and mortgage loans. The company guarantees that a Priceline.com mortgage is the "lowest-cost loan on the market" and backs this up by paying $300 to any customer who finds a…