I'm 99% certain it was Top Gun, and also, IIRC, it was because it had a Pepsi ad bundled with it before the movie (a somewhat groundbreaking move at the time). That subsidized the 'cost' of the movie on tape, reportedly.

EDIT: looked a bit more. Diet Pepsi, not Pepsi, and it was 1986. Article I just found said it was only dropping the price from $29 to $26, so the bigger price drop was likely/possibly something else before that. My memory was that that Top Gun / Pepsi thing was the big deal that changed the VHS pricing, but it's been 30+ years so I'm likely misremembering...

EDIT 2: maybe it was TG after all... https://www.everything80spodcast.com/how-the-top-gun-vhs-cha... ?