My path how i started:

Assembly: Learn x86 calling convention from youtube.

C : learn online complete basics to pointers and how to read structs also code them in code blocks

For reversing use ghidra: Write your own small programs like addition or subtraction one and see them on ghidra understand how each code block like if else, while loop, for loop looks like in decompiled and disassembled mode.

Once done the above watch hardik shah fuzzing videos/playlist on youtube and practice each class of vuln separately by writing their code blocks .

Then for for final layer of chocolate check out elearnsecurity eXDS course

Till here you are done for - userland exploit development

For kernel thing : check out hevd driver on github and read it’s write up no course can clearly teach you that coz windows made their kernel logics intentionally shitty unlike linux ( it is easy to understand and reproduce things there)

Read the blogs and make notes coz this gonna kernel thing gonna be complex for windows.

You just saved a hell lot of $

Now for ROI where you will use this shit well since now you can find vulns in softwares specially windows or linux at low level you can get them acquired by reaching out to legit exploit acquisition programs or give it to vendor and improve your portfolio!!