"You bet you"? That's the closest I could think of. Or is it "you bet yourself", with the "self" omitted so it's quicker to say? Or is it something else altogether?
I find this undocumented but fairly compelling:
You betcha-- Contraction of "you bet your...." (life, ass, money, etc.). Also "you betcher", as in You betcha! or You betcher ass!
A lot of people in Minnesota and the Dakotas (where they also say this frequently) are of German or Norwegian background. My theory is that it might have come from one of those languages. Perhaps in the German or Norwegian languages there is comparable saying, and "you betcha" is how people have translated it into English.