Ya can hide your incessant love for the 'Karp all you want, 'cause ya ain't foolin' me. You definitely got the hots for Magikarp. I would know.
Damnitt these gay roleplays are too frequent Only one Magikarp. ;D
How much rarer?
... Good question.
Let's put it this way. There probably ain't more than 5 vintage shiny 'Karp on the entire trader's market... if any at all. I'd imagine a five-of-a-kind unusual would fetch a pretty penny, no?