There's going to be a big difference between something signed by Kentarou Miura and something signed by Nobutoshi Canna. I'm guessing Canna has signed a lot more autographs over the years, but that's just an assumption.
In any case, items signed by Miura are somewhat rare and have become quite pricey these days. If you find one that's cheap by your standards, it's likely fake. And if you were asking for something signed by both men, I don't think that exists.