Hi @useruk1
First you must know that to use Power Apps and Azure you must have a subscription to each, and ideally they should be in the same tenat
Now you can use as mentioned in the other post development environments but you must have a Microsoft subscription to do so. It is important to note that these environments are not productive or sandbox and are limited in terms of the functionality you need to develop, if what you want is to train in this technology can serve you if on the contrary you need to make developments to pass them to production is not convenient to use this type of environments.
Now to answer your question you must have in the case of Power Apps a Power Apps premium license that has a cost of 20$.
That cost will include database storage space and the possibility to use premium connectors and dataverse.
Now development, test or production environments don't have a cost as such, but they take up storage space that is deducted from the total you have. For example, a dataverse environment takes up about 2.1GB of space, so having 3 would be 6.3 GB, then you must take into account the growth of your database.
Additionally for each license there is an increase of space. You can also buy space but it is very expensive.
As I said at the beginning, depending on your needs you can opt for the Developer Plan or a subscription.
As for azure it works the same way, here are some links
Power Apps Developer Plan | Microsoft Power Apps
Power Apps Licensing, Pricing & User Plans | Microsoft Power Apps
Azure for Students – Free Account Credit | Microsoft Azure
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