When Toyota introduced its Lexus Div. five years ago the big question was, "Can it build a luxury car that will sell in the U.S.?" The big question today is, "How is Toyota holding the price on the Lexus?" The '95 top-of-the-line LS400 now is arriving in showrooms carrying a $52,000 sticker, the same as the '94 model. That's a $17,000 bump in five model years-it debuted in August 1989 as a 1990 model carrying a $35,000 price tag. But some critics say the pricetag should have jumped an additional 5% to 6%, or $2,500 to $3,000, based on the appreciation of the yen against the dollar. They charge that Toyota is stoking the sticker to keep Lexus from losing market share to other foreign luxury cars. "Phooey," says George Borst, group vice president and general manager of the Lexus Div. "Should the price have been higher? Half the people say the LS400 is priced too high, the other half say we haven't taken enough of a price increase ... Five years ago when we came out with the LS400, the Europeans didn't take us seriously, and now they're bringing out new products and dropping their prices to compete with us." Toyota was able to hold prices on '95 options at 1994 levels because of massive cost-cutting over the last two years that helped offset currency fluctuations, he says. (The only increase was a $10 bump in freight charges