Blockbuster used to cost a Euro per day. 1.50 for new releases. Renting something from Amazon costs 3.99, about as much as buying a used DVD. I don't think that's a fair price.
Alita: Battle Angel is $5.99 to rent in HD right now on Amazon.
Redbox is charging $2.12 for all Blu-ray releases on disc, including Alita. Their streaming version is also $5.99 in HD.
Hard to imagine running those kiosks 24/7, maintaining them and stocking them is cheaper than serving up a stream version. They're no doubt charging $5.99 because they're confident that they can command it based on convenience (laziness factor). $3-$3.50 for a new release in HD is around the edge of reasonable in my opinion; and $1 to $2 for everything else.
I know someone that owned a rental chain (the old style physical stores) in the 1980s and early 1990s. At any given time 15-20% of their sales came from late fees. Also interesting is that VHS tapes once cost $70-$100 ($40-$60 wholesale; $55 in 1984 is $140 today), so there was a serious investment and risk in renting them out to customers at the time. Stores typically purchased the tapes outright from the studios back then (so you can imagine the VHS tape inventory costs); more recently many independent stores switched to a shared revenue model, where they didn't have to front cash for inventory.
Blockbuster was also running bricks-and-mortar stores, and buying physical DVDs, and replacing them when they broke/wore out/weren't returned. A digital "rental", on the other hand, has basically zero marginal cost.