Mr Mansfield is arguing there should be a stay of proceedings because the Crown - on behalf of the US government - adopted a "starve out" policy which restricted Dotcom's funds being used to recruit US technical and legal scholars to help his case.
Mr Rothken said they would need about US$500,000 to get the people they needed and it could take up to six months to gather all the evidence required from them.
Trying to find experts to contribute for free had been "futile", he said.
"With the complexity of this case and the time and effort for travel, that's the reality," said Mr Rothken.
However, one high-profile figure had agreed to help.
Professor Lawrence Lessig - a world-renowned copyright expert currently running for president - had provided an affidavit outlining his views on the case.
His attempts to replace Barack Obama at the helm of the most powerful country in the world might make his appearance before a New Zealand court difficult, Mr Mansfield said.
Mr Rothken said the defence would also engage technical experts who could look at the metadata taken from Mega servers.
The Crown told Judge Nevin Dawson there had been 10,000 take-down notices made to Dotcom's website which were ignored but Mr Rothken said they had neglected to mention 10 million that had been complied with.
"The expert will say that's over 99.99 per cent compliant and not a prima facie case as a matter of law," he said.
Dotcom is expected to give evidence after Mr Rothken.
The hearing continues.