The idea here is that this spell can prove benefecial in a number of situations due to its strange flashback cost
She is especially devastating in the OP13-002-portgasdace matchup and the OP11-041-nami mirror, where both decks often build huge hand advantage through Card and Leader effects
Its value depends on its condition, market demand, and language (Japanese versions may be more valuable)
And you can easily find the right price by browsing sold listings of that card, and because Pokmon cards sell a lot on eBay, that shouldnt be a problem for you
This would feel better were it not for the fact that they completely removed random card rewards at the end of winning a match, meaning this is now your way for getting that sort of thing
The difference between paying market price and getting 2030% below is usually just showing up at the right time and knowing which stores to look at