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For artists starting out, or not making enough so that such an investment can be easily written off — there are a) 30 day free trials, and b) a ton of vastly cheaper and even free alternative digital painting tools ranging from Manga Studio to Corel Painter down to Gimp, Paint Tool SAI, and so forth.
I would absolutely recommend finding cheaper and even free alternatives to the Adobe suite of software for digital art production. In most cases you can find an app that works exactly the way you want; created by a single coder or small development team in the indie space. Supporting indie devs in this way is not only karmically advantageous but you can also get a lot more exposure from showcasing your work using tools that are in a more narrow circulation.
Using some big and definitive platform-tool like Adobe can also hurt your creativity in some ways because the scale of the platform and it’s age means that you are locking yourself into working the way that an engineer decided twenty years ago. The best example of this is the difference in layer masking between Pixelmator and Photoshop.
In any case, always, buy the license if you’re using the software.