Thanks for letting us know. In order for us to investigate please can you provide an example title (or two or three) and let us know in which country you are located and from which Amazon store the prices are being displayed (US, UK, Germany, Japan etc).
I am not sure it's what what Karla is referring to, but I've noticed a little, 'which-coconut-is-the-ball-under' price list shenanigans over at Amazon's site, but if you look at The Revenant's IMDb page, it offers the Amazon (US) price as $4.99.
So it's an Amazon thing, and a sneaky thing at that! It makes it look like IMDb is in cahoots, though...so it's definitely worth looking at, even if not related to what the OP reports.
This is tricky to solve ... the prices on IMDb are correct -- you just need to click the "More purchase options" link on the Amazon site to access the cheaper SD options. In your example
bluesmanSF, Champion
https://www.dropbox.com/s/4qm2ulkwcxibooi/Screenshot%202016-07-05%2003.08.27.png?dl=0
When you click the option, the list shows a lowest price of $5.99,
https://www.dropbox.com/s/rgwqnphnykcklcl/Screenshot%202016-07-05%2003.12.04.png?dl=0
but there is a 'more options' link offering the lower definition version at the price shown on the IMDb page.
https://www.dropbox.com/s/z1eabtcmnoi97hy/Screenshot%202016-07-05%2003.12.42.png?dl=0
So it's an Amazon thing, and a sneaky thing at that! It makes it look like IMDb is in cahoots, though...so it's definitely worth looking at, even if not related to what the OP reports.
Col Needham, Official Rep
Col Needham, Official Rep
Col Needham, Official Rep
"From $4.99 (SD) on Amazon Video"