In a surprise move, Honolulu Councilman Donovan Dela Cruz announced today that he is dropping out of the race for Honolulu mayor and instead will run for former state Sen. Robert Bunda’s seat.

Dela Cruz cited economic hardship in his decision to withdraw. His campaign had felt “the financial pinch.”

“While my desire to serve the public remains, my mayoral campaign does not have the necessary funds to allow me to spread my vision for the City and County of Honolulu. Looking at this mayoral race realistically, and being honest with myself and my supporters, I have decided to take a different path,” Dela Cruz said in a statement.

Bunda vacated his seat to run for lieutenant governor. He represented District 22, which covers mostly Oahu’s North Shore. The district was part of the area Dela Cruz represented on the City Council.

Dela Cruz, who is 37, is at the tail end of his second four-year term as a city councillor and was term limited. He filed his nomination papers on Thursday and joins three other Democrats seeking Bunda’s seat, including state Rep. Michael Magaoay. A Republican is also running in the race.

Dela Cruz’s departure from the mayoral race means there are now four candidates competing in the special election to serve the remaining two years of former mayor Mufi Hannemann‘s term. Hannemann stepped down July 20 to run for governor.

Acting Mayor Kirk Caldwell, former Honolulu prosecutor Peter Carlisle, University of Hawaii professor Panos Prevedouros and City Councilman Rod Tam remain in the race. The candidate most affected by Dela Cruz’s withdrawal is Prevedouros. He is the only anti-rail candidate in the race and would have benefitted from a split vote. A candidate needs only a plurality of votes to win the special election, to be held on Sept. 18, 2010.