(Reuters) - Visa Inc is buying Earthport Plc , which provides cross-border payment services to banks and businesses, for 198 million pounds in cash, a unit of the U.S.-based payments network said on Thursday.Visa International Service Association's offer of 30 pence for each Earthport share is about four times the stock's closing price of 7.45 pence on Monday.(This story corrects an earlier version to remove extraneous word in paragraph 1)