When streaming, free with subscription is fine, free to own is better. Second best is $0.99 to buy a digital copy.
I used to have a deal alert saved on slickdeals for “free google play”. It worked for a while, each week I would receive an email listing all the free movies and songs that were currently for sale on google play. Eventually, I had to kill the deal alert when the notifications were taken over with device offers and free shipping.
I have found a replacement with JustWatch.com and their search filters. The following link searches Amazon Video for anything under $1, then sorts it by items that recently received a price drop.
The search results are very much “bargain bin” worthy, but there are some real gems in there if you like wacky B movies. I do!