How can they afford fuel on 8k per month?
- They only make liveburns a few times a year.
- They experiment with different cheap fuels. One rocket ran on rubber and actually worked quite well.
- They're quite known around Denmark, so they get unbelievable prices on fuel from companies that want to be associated with the project.
There is not the slightest difference between natural and synthetic fuels. Either one can be toxic or not.
And good luck even defining "natural". Crude oil is natural - so I guess it gets a free pass? Uranium is natural too.