Presidential Funding Act of 2003 - Amends the Internal Revenue Code (including the Presidential Election Campaign Fund Act and the Presidential Primary Matching Payment Account Act) and the Federal Election Campaign Act of 1971 to, among other things: (1) increase the presidential primary $250 one-to-one match to a four-to-one match; (2) increase the presidential primary qualifying threshold of $5,000 in 20 States to $15,000 in 20 States; (3) require candidates to be eligible to receive funding under the Presidential Election Campaign Fund Act to have received payments under the Presidential Primary Matching Payment Account Act; (4) revise candidate expenditure limits, including permitting the national committee of a political party to make expenditures in connection with the general election campaign of any candidate for President of the United States who is affiliated with such party in an amount of up to four (currently, two) cents multiplied by the U.S. voting age population and permitting an eligible candidate for the office of President of the United States to receive payments from the Secretary of the Treasury of up to $75,000,000 with respect to a campaign for nomination for election or of up to $75,000,000 with respect to a campaign for election to such office; and (5) double the three dollar presidential campaign tax return check-off to six dollars.