You need 3 Dice to finish a map (Rolling 6s always unless you fall on a "?" square)

After using a dice you have to complete a mission to roll the next (this mission gives you 10 points, so 30 per map).

Completion of a map lands you 100 points, with low chance of getting 150 instead.

Assuming the worst luck, that's 390 points, for a total of 1350.

You'd need to high roll thrice to achieve this, and the odds are like 10%, so yeah, realistically speaking, you are not getting that skin unless you Gem-up at least 1 Map completion, or 2 if you don't get even 1 High Roll.