The 'Official' game guide says not to buy this expensive Pokemon when they are so easy to catch. I just got the new Nintendo Power #184 (FR/LG on the cover) yesterday and it has a begining walk thru for the game. The magazine says:
Is there something special about this Magikarp that warrants paying for it and leveling it up to level 20?
Patience Pays Big
A shady-looking man in the Pokemon Center near the Mt. Moon entrance will sell you a Magikarp for $500. If you're patient enough to raise the Magikarp to Level 20, the Gyarados it evolves into will be well worth the investment.
Is there something special about this Magikarp that warrants paying for it and leveling it up to level 20?