If you don't have a B737 type rating, then yes, the only way to apply is through the cadet scheme.
Ryanair have a huge cadet scheme in operation with as many as 4000 pilots currently waiting to part with 30000 euros for a 737 type rating. Therefore unless you're willing to self fund your type rating, then I'm afraid Ryanair won't touch you.
Going along to one of their open days might give you a bit more information than that available on this forum.
Good luck whatever you decide.