Inquiries about purchasing SSL certificates - Where would be a good SSL certificate server? (Cost, Speed)

I want to set https in the mobile app (hybrid type). I want to purchase SSL certification, but the price is 200,000 won to 500,000 won/year I heard that there is a difference in the speed of going to the authentication server depending on the price. If you recommend one of your authentication servers, it will help you decide. Thank you!