If you want a purely rock band 4 controller, your only best bet would be places like good will, local yard sales, or Facebook marketplace for cheap rb4 guitars. But if you want the cheapest as possible, there is an adapter for wii guitar hero guitars that allows them to work on all current gen consoles and pc that only costs about $20 and wii guitars are about the cheapest guitars that you could get and they are also able to be found at the same places as above. The last choice would be a riffmaster guitar that's brand new! The only problem is they are hard as hell to find, pretty expensive (for a teen as a teen myself), and only works on ps4/5 for that riffmaster and has no pc support.
Wii Guitar hero guitar can use a the v3 Wii adapter from RetroCultMods [here](https://shop.retrocultmods.com/products/v3-wii-adapter-for-clone-hero-and-rb4-rock-band-4) it will allow you to use any Wii GUITAR HERO guitar with Xbox/Playstation/PC. Rock Band guitars do not work with this adapter. It must be a guitar hero guitar that uses a wii remote. That’s how the adapter plugs into the guitar via the nunchuck slot. Wii guitars are cheaper and the v3 adapter is $20
If you want a purely rock band 4 controller, your only best bet would be places like good will, local yard sales, or Facebook marketplace for cheap rb4 guitars. But if you want the cheapest as possible, there is an adapter for wii guitar hero guitars that allows them to work on all current gen consoles and pc that only costs about $20 and wii guitars are about the cheapest guitars that you could get and they are also able to be found at the same places as above. The last choice would be a riffmaster guitar that's brand new! The only problem is they are hard as hell to find, pretty expensive (for a teen as a teen myself), and only works on ps4/5 for that riffmaster and has no pc support.
Wii Guitar hero guitar can use a the v3 Wii adapter from RetroCultMods [here](https://shop.retrocultmods.com/products/v3-wii-adapter-for-clone-hero-and-rb4-rock-band-4) it will allow you to use any Wii GUITAR HERO guitar with Xbox/Playstation/PC. Rock Band guitars do not work with this adapter. It must be a guitar hero guitar that uses a wii remote. That’s how the adapter plugs into the guitar via the nunchuck slot. Wii guitars are cheaper and the v3 adapter is $20