Mimic Amazon Add on item with certain amount purchased

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I have a pokemon TCG store, and want to offer people the chance to add on ultra pro penny sleeves, top loaders, etc to take care of the cards only if they meet an order minimum of 25$.  How can I enable that "rule" and allow an addon to then be purchased?  Alternatively is there a way that it is listed at X price, then when it gets to 25$ it becomes a lesser price?