D.E. Shaw & Co. is making it more expensive for investors in its biggest hedge fund, raising fees while many of its rivals have been forced to slash them. The New York-based investment firm is reverting to a fee model that it held for the better part of the 2000s, according to a person with knowledge of the matter. The new structure will charge 3 percent of assets and 30 percent of profits and will take effect at the start of next year. The move cements D.E. Shaw’s standing as one of the pricier funds in the industry.