These are the prizes given to you for collecting mini medals.

Item Number	Number of Medals Needed	Item Received
001	4	Thief's Key
002	8	Mercury Bandana
003	13	Bunny Suit
004	18	Jolly Roger Jumper
005	25	Transparent Tights
006	32	Miracle Sword
007	40	Sacred Armour
008	50	Meteorite Bracer
009	62	Rusty Helmet
010	80	Dragon Robe And Captain Pose

After you get the item for 80 Mini Medals he will start selling you items:

Prayer Ring	3 medals
Elfin Elixir	5 medals
Saint's Ashes	8 medals
Reset Stone	10 medals
Orichalcum	15 medals
Pixie Boots	20 medals