Give your right arm for something/to do something
Definition 1 of 1
Pro Tip 1/3Idiomatic Intensity
Used to express intense desire for something, emphasizing willingness to sacrifice greatly. 
She would give her right arm to meet her favorite author in person.
Pro Tip 2/3Non-literal
This is an idiomatic expression and isn't meant to be taken literally; it's about the strength of feeling. 
I'd give my right arm for the recipe to this incredible cake.
Pro Tip 3/3Informal Speech
It's a colloquial phrase, best used in informal settings and not in formal writing or speeches. 
For tickets to that concert, I'd give my right arm.