Ability - every 60 seconds you can gamble for an item every level increases the chance for and quality of item.
Gamble chance - there is a base chance of 16% of getting an item. Every level adds 0.6% chance of item. Level 1-33 only common items. Level 34-66 common and uncommon at a 60/40 split. Level 64-99 common, uncommon, and rare at a 50/30/20 split.
Gamble cost - gamble will cost you $5000.
Ability - do you think the ability should scale with the speed or should it stay at a 60 sec cool down. Ability would be activated similar to Mr Iron maybe with a confirmation screen or a double tap.
There may be some balancing of cost and cooldown time but the base idea is there.
Other thoughts is that there could be different levels of cost allowing someone to choose the max rarity of item they want so I can just try to get at most an uncommon item to find a certain card ie last train of the day