Platforms like Netflix , Hulu , or Disney+ offer "Data Saver" modes that provide efficient compression (similar to the 300MB goal) without security risks.
Forums like (historically) ReleaseBB or DDLValley (successors) often have sections labeled "Area 18" or "Exclusive HD Zone." These require registration and usually have a "like-to-unlock" link system. hd movie area 18 300mb new