3 tier system would be good eg. When you open the bottle you get the choice of either 1.easy, 2.medium or 3.hard, the rewards are equivalent to each.
Easy = close distance / reward (green/blue upgrade) low amount of loot
Medium = medium distance / reward (blue/purple upgrade) medium amount of loot
Hard = long distance / reward (purple/gold upgrade) large amount of loot
my two cents....Bobs your uncle, everyone is happy.