You can always use the tried and true Just Steal method, where you yoink art from twitter or pinterest thats close enough to what your mental image looks like. Of course, dont do this if you're running a show.
AI-generated character art. If you put in the time to tune the prompt (or just keep rerolling) you can get some really good results that way. It's harder for female characters because it always wants to add giant gazongas, but eventually you can get it to generate a normal looking character.
MTG cards. There are a wealth of them out there with many different art styles and styles of fantasy.
I would still think that AI generator are the easiest. Stable diffusion is free (as in free speech, and as in free beer) and runs on your own PC provided you have a GPU. You can check the !imageai@sh.itjust.works community to get some ideas on prompts and the kind of result you can get.
Then there is learning to draw, but expect a couple of years of classes, but someone who went from "can't draw to can draw a character" know betters how much time is needed