As a final decision, I've chosen to redo the coin item settings one last time.
Before
1day, 1week, 1month items had 1/2 the stats of a 1year item.
1day, 1week items had a fixed price of 2,000 coins.
1month items had a fixed price of 8,000 coins.
1year items had a fixed price of 84,000 coins.
Now
1day, 1week, 1month, 1year items all share the same stats.
1day, 1week, 1month, 1year items' prices all vary depending on the item.
Prices are determined by the physical look, stats, and time length of the item.
Examples
Head
Price of Direfang:
1week, 2,000 coins
1month, 13,000 coins
1year, 33,000 coins
Price of Goldie:
1week, 2,000 coins
1month, 13,000 coins
1year, 27,000 coins
Wings
Price of Raptor:
1week, 3,500 coins
1month, 23,500 coins
1year, 53,000 coins
Price of Delta:
1week, 3,500 coins
1month, 23,500 coins
1year, 48,000 coins
Mini-Bots
Price of Waddy:
1week, 3,000 coins
1month, 15,500 coins
1year, 39,000 coins
Price of Taurus:
1week, 3,000 coins
1month, 15,500 coins
1year, 41,000 coins
Flags
Price of Dragon:
1week, 3,000 coins
1month, 15,500 coins
1year, 44,000 coins
Price of HeartBalloon:
1week, 3,000 coins
1month, 15,500 coins
1year, 41,000 coins
Transformation
Price of DigiDragon:
1day, 2,000 coins
1month, 31,000 coins
1year, 76,000 coins
Price of General Scourge:
1day, 2,000 coins
1month, 23,000 coins
1year, 57,000 coins