i downloaded unreal and basically everything costs over 25 dollars, for some loving materials it costs 25 or even a few models
git gud
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Seriously though. Models are easy to convert into Unreal's format. They take a bit more work than Unity, since they want you to provide lightmaps for static meshes and proper rigs for skeletal meshes, but these things mean you models are far more optimised and will give better performance in the long run.
Materials are really simply to do, since they're physically based. You can create a new material in the content browser, double-click it to open the Material Editor, and use some visual scripting to make any material you want. Hell, download the Unreal Content Examples pack from the "Learn" page (it's completely free), and then open up a new map with that and go through their materials. You can get a really cool picture of how they make things like bronze, glass, grass, wood and so on. They also have a great series of YouTube tutorials which take you through basic concepts like using LERPs, Multiplys, parameters and UV Coordinates with textures to make some really awesome materials from scratch.