Bum Jr. got 3 years of absolutely GREAT pitching instruction from a D1 pitching coach by purchasing a package deal where he grouped up with 2-3 other kids. The best package deals were in the Spring and Fall and it averaged less than $20 per session. Video and one-on-one feedback was part of the deal.
I would recommend such instruction starting about age 14 and not year-round but in increments perhaps twice per year, in 10 session packages, ideally. It's all about the quality of the instruction. You can pay $100 per session for terrible instruction or $15 per session for fantastic instruction, or vice-versa.. it's all about networking and finding the best deal. There's not necessarily any correlation between quality and price, so do some shopping.
Importantly, by doing it in increments twice per year, it provided affordability but also helped Bum, Jr. "fine tune" periodically to avoid bad habits.