"mini planes that fly"... that doesn't require a jet engine, and certainly not one built from scratch. As many have already mentioned, building a jet engine fr

"mini planes that fly"... that doesn't require a jet engine, and certainly not one built from scratch. As many have already mentioned, building a jet engine from scratch isn't exactly easy or cheap. In your position I would get a battery, electric motors, propeller, microcontroller and a 3D printer, then figure it out from there. I know it's probably a bit off from what you wanted, but it's a "cost efficient" way to actually built something. Once you have something flying you can upgrade from there... I am currently in the process of building my own drone from scratch this way, designing the drone and programming the remote control, flight controller completely myself... it is/was a lot harder than I expected. So, what I am trying to say is: don't be afraid to use of the shelf components and don't make things harder than they have to be. Get started, then get creative. Just my experience with this.