I think you mean 30 billion. The entire GDP of the US is only 16.77 trillion and the entire revenue of the US government is only a fraction of that. Both the Apollo project and Manhattan project were around .4% of the GDP. A lot for a single project, but not what I would consider a "significant part". Social Security is an order of magnitude greater.
This was a significant part of GDP and please also consider that the US had a much smaller population to bear the costs.