50 x Grilled Fish will sell for 520,000 Star Coins!  
9 x 50 Grilled Fish = 4,680,000 Star Coins
42 x 50 Grilled Fish = 21,840,000 Star Coins

Items:
42 stack of 50 Grilled Fish

I will come to your Valley with my full inventory of Even More Miraculous Pickaxe Polish.
This is safer method and I do not need to login to any accounts.  I just come to your Valley with the Even More Miraculous Pickaxe Polish in my Inventory and will drop off the bottles on area near your Valley Visit Station.
After I leave, you can sell the bottles at Goofy's little shop.