A more affordable idea that I came up with was to make a lightweight frame (maybe pvc) to support a bunch of big weather or mylar balloons. The frame wold then be covered with ripstop nylon to keep the balloons secure and protected. Then below the frame you could mount a seat and a small engine or motor attached to a prop made of pvc similar to this instructable but reversed: https://www.instructables.com/id/PVC-pipe-blades-and-rotor-for-HAWT-from-scrap/ Then you could have a steering wheel attached by some line to a rudder on the back for steering. To keep it small you could make there be less balloons so the aircraft is slightly heavier than air causing it to not float without help. This makes it so you don't end up floating off if your engine goes out or the balloons heat up becoming less dense. After that you just add another engine facing down to give you that last boost into the sky. Just remember though to MAKE SURE EVERY FITTING IS AS SECURE AS POSSIBLE. I would use pvc cement and get it real tight then put bolts through them. Also if you do this please post some pics or an instructable. Give me credit if you use my idea. Excuse my drawing I know it sucks.