McLuck's Jackpots have four tiers: Mini, Minor, Major, and Grand. Each tier has a different minimum starting amount, and the progressive Jackpots can grow as players contribute.
Gold Coin Jackpot minimums:
Mini: 10,000 GC
Minor: 200,000 GC
Major: 2,000,000 GC
Grand: 200,000,000 GC
There is no maximum win limit for any Jackpots tier.