41. Are there limits on the amount a candidate can spend?

Paragraph 9004: The aggregate payments to which the eligible candidates of a political party shall be entitled under subsections (a)(2) and (3) with respect to a presidential election shall not exceed an amount equal to the lower of— (1) the amount of qualified campaign expenses incurred by such eligible candidates and their authorized committees, reduced by the amount of contributions to defray qualified campaign expenses received and expended or retained by such eligible candidates and such committees, or (2) the aggregate payments to which the eligible candidates of a major party are entitled under subsection (a)(1), reduced by the amount of contributions described in paragraph (1) of this subsection.

United States Code, Title 26, Internal Revenue Code. 

Spending limit however only apllies to presidential candidates who accept public funds.