Need help with a d20 campaign

Hello, everyone! So, in the midst of creating my own campaign, I have run into a snag. For context, the setting of the world is a low-magic world a la "Conan the Barbarian" / "Kull the Conqueror" / "Turok: Son of Stone". Thing is, I do want -some- magic classes to balance out the physical classes (Barbarian, Fighter, etc). I have looked at both Pathfinder and DnD 3.5 sources and did not find anything that satisfies a way to keep casters "low-magic". Are there any third party sources out there that could be used that use the d20 system?

I'm sorry Andrew but this thread is off-topic for our site. When you signed up for Roll20 you agreed to abide by our Code of Conduct and this post violates the Intended Use section of the code. Since this is a question about roleplaying game mechanics, you’d be better served posting it on a general RPG site, like reddit/r/rpg . I will have to move this to the archives which closes the thread.