"If you believe that George acted properly in self-defense; if you feel he is being wrongly prosecuted; if you feel that George deserves a fair trial, please consider sending one last donation," attorneys Mark O'Mara and Don West said in a blog post ahead of the trial's June 10 start date.
Zimmerman, 29, is charged with second-degree murder in the shooting death of Trayvon Martin, 17, in Sanford, Fla., Feb. 26, 2012.
Zimmerman, a neighborhood watch volunteer at the time of the shooting, has maintained he acted in self-defense after being attacked and beaten by Martin, while the prosecution contends Zimmerman targeted and pursued Martin because he was black.
The defense's trust account has less than $5,000 and more than $20,000 in liabilities, Zimmerman's attorneys said in the blog post.
The fund had more than $300,000 in January.
"We've calculated that we need another $120,000 to give George the defense he deserves," they said. "At the barest minimum, we need $75,000 to give George a fighting chance."
The money will be used to pay experts and for deposition transcripts, O'Mara and West said, explaining they themselves "have not been paid a cent for their services" and their legal interns work for free.
Zimmerman and his attorneys have sought donations for his defense since early in the case.
On Tuesday, Circuit Judge Debra Nelson rejected a defense request to delay the start of the trial. She also said the defense could not mention Martin's marijuana use, history of fights or high school suspension during opening arguments.
She additionally denied a request jurors be allowed to visit the gated townhouse complex where Martin was shot, calling it a "logistical nightmare," denied a request attorneys for both sides be prevented from talking publicly about the case and refused to sequester the jury pool, which could number 500 people, during the selection process.