There is a lot of competition in cloud services. While price has traditionally gone up with demand, the rule mainly applies to scarse resources where the limited supply will drive the prices up. With software this will only somewhat apply on an uneven field without proper competition (and even there for different reasons).
The running and support costs of a cloud service will go up with increased usage, however it's only a small part of a software conpanies expenses and other areas will not increase. Unlike with scarse resourses increased sales will lower cost pressure for a software company as they will end up with relatively larger net revenue. It's the opposite of a traditional field where increased demand could increase the cost of the raw materials or require investments in manufacturing, storage and shipping (and larger inventory).
Its quite the opposite, the more that use computing resources, the cheaper it becomes, why do you think there are massive compute clusters for research and such?
As i was saying the problem isnt to do with supply. As technology gets better, things like cost per GB, cost per B/s and other things get much cheaper, but as i was saying companies dont really care about supply demand graphs anymore, they care about profits. So to maximise profits they take supply out of the equation. A lot of places are starting to use algorithms to set prices and the main factor is profit, so while the pricing appears to follow the supply demand economics in truth this isnt so. This is because if you had an unlimited supply the algorithm would raise/lower prices depending on demand only, so if a lot of people are buying the price is increased, if very few are buying the price is decreased to encourage sales.
For example online backup services could offer 100GB to everyone, they may not need to have 100GB physically available for everyone but as the usage differs, they only need to have enough to fit the average use. Hence why i was saying that supply does not matter.
take gas prices for instance, there is a lot of supply currently (despite it being a limited resource), yet fuel costs many times more than it did 2 decades ago, much more than the rate of inflation. Its not the supply, its the demand and that the companies involved all focused on maximising profits instead (besides many of the companies had government links, so the money went to their origin governments). Now algorithms are used to determine the price of fuel at the hour based on how cramped the gas station is at that time, to determine pricing of items for different individuals based on their willingness to spend.
As i said its designed to take all the money it can from you. Implementing this sort of economic practice has a serious price to pay however as there is a defined finite amount of wealth. It will get to a point where money just becomes worthless. I always say that the more overpriced an item is the less valuable it actually is.
There also needs to be a decently priced online service with decent backup space as this is something that would expect regular payments. I find many NASes to be priced too high for the average consumer which leaves a gap filled by routers nowadays.