Hi @Luftbauch,
The idea is that the assets themselves will always remain FREE! but the prices mentioned above are a part of a collective tip/donation system to either be powered by Patreon.com or directly through our website at patreon.binarysword.com which is currently in development.
Think of it this way,
The more collective money we receive on a per-month or per-release cycle will allow us to provide larger ‘Asset Crates’ which will be offered FREE! for all the UE4 Developers and well the community at large if we cannot release directly through the UE4 Marketplace.
An example of this is that we release say a Weapons Crate valued at around $1,000 USD for FREE! on either the UE4 Marketplace or our own marketplace, now lets say that 100,000 people download that Weapons Crate for FREE! but the Weapons Crate is after all valued at $1,000 USD (not marketplace equivalent but exclusively commissioned rates) that we would only need 1,000 people out of that 100,000 to provide $1 USD each to raise the $1,000 USD needed to create that Weapons Crate 
Now obviously we could be making a lot more $$$ if we were to charge for the content per-person at UE4 Marketplace’s average prices of between $5 to $100+ per-asset crate/pack BUT we believe strongly in supporting the developer community and those with money to spare can help those without, by pledging as low as $2 USD (the price of a cup of coffee) on our Patreon or website page to support the development of these FREE! Asset Crates.
[HR][/HR]
We also understand that we may very well raise $0 on a per-month or per-release basis and if that is the case we will still release FREE! Asset Crates here and there BUT we will not be able to provide customised content specifically for the developer community and instead we will just release assets when we can that were created for our internally focused projected (FPS & RTS games).
Some of the team might also pitch in with some of their own personal assets they have created in their spare time but that is a BIG MAYBE.
Because at the end of the day we need to eat… and have coffee… LOTS OF COFFEE 
&stc=1