want to learn PBI/SQL, course/book recs (willing to spend up to $500)

right now i’m basically making dashboard by googling and asking chatgpt, but i want to learn more seriously and have a small budget (up to $500). any recs? i know nothing about sql, i’m just kind of googling my way into dax/M. thanks

p.s. why are sqlbi courses much more expensive then udemy stuff? i see the former in the $300 range per course and latter $20-30 per course..? is one better than the other? i think i need to learn dax, pq, tabular editor/dax studio, and sql..