Priceline said late Thursday that it would buy Kayak Software for $1.8 billion, sending shares of the smaller online travel firm soaring after the market close. Kayak also reported third-quarter earnings and revenue that handily beat expectations. In a deal that surprised analysts and investors, Priceline (PCLN) will acquire Kayak (KYAK) for $40 a share in cash and stock. Kayak shot up 26% to 39.18 in late trading. It had fallen