Here, you can find exactly what you need to start building a good paper airplane, or how to fine tune your gliders.
Note: There are not very many cheap kits available online. Competitors may be better served making a glider based off of planes found at sites like https://www.hippocketaeronautics.com/
Very expensive and hard to make, but the gold standard in terms of performance
Half the price of Freedom Flight, easy build
Easy to build, cheaper, mediocre performance
A fun resource including a flight simulator, a virtual rocket lab, and a gallery of airplane designs.
A Youtube channel with lots of interesting videos on different planes.
A Youtube channel similar to Mustard but focusing more on logistics in general, including how airlines choose to fly to certain destinations, how aircraft carriers work, and the economics of transportation.