Conservative radio talk-show host Rush Limbaugh Wednesday inked an eight-year contract for around $400 million, underscoring how radio is spending big sums on bankable talent to compete in the crowded entertainment field.

Mr. Limbaugh's compensation of $38 million a year, plus a signing bonus of about $100 million is less in absolute terms than the five-year, $500 million contract Howard Stern cut in 2004 with Sirius Satellite Radio Inc. But Mr. Limbaugh's contract could net him more, as Mr. Stern must pay costs for his cast...