A: Use YouTube with the "Data Saver" option (Settings > Playback > Data Saver). You can also use Snaptube (legal version) or NewPipe to download legal YouTube videos at 144p or 240p, which will be smaller than 100MB for a movie.
18;write_to_target_document1a;_tXTsac-xNNKO4-EPiMbCwA4_20;a5; 10xmovie 300mb