Think back to the early days (if you're old enough). All you got was a silver film. Adhesive had to be sprayed on, luckily before my time too.
Then there was the dyed polyester. Great to look at, but turning purple within a short time.... and still sold today at places like Repco and Supercheap as well as Trade Me and of course the cheap car tinting places.
Fortunately, some of us have moved on from this and offer genuine performance films.
Today's window film uses the latest technology and consequently is more costly to produce. The latest low-e film contains Gold and manufacturing plants had to increase security, for obvious reasons.
So why on earth are some people still going with the cheapest price??????
As the saying goes: "You get what you pay for"
Granted, just because one price is higher than another, does not guarantee a superior product. Therefore, ask questions.