Accessible apps which offer voice lessons?

Hello,
I am in my church choir.
Recently, I was having a conversation with my mom & she suggested I take voice lessons.
I've been trying to conduct research about the most accessible and budget friendly options for accomplishing this task. I almost always have my iPhone &/or iPad with me, wherever I go.
To that end, I was wondering if anyone knew of an accessible budget friendly app, which would give me voice lessons?
Any and all suggestions are welcome.