That's a really tough one to balance, because, while it's true that you played for 59 minutes and only got a score of 250k ish, it's possible to beat it in 20 minutes and get a score of over a million (for example). And like you said, you can continue at different points. Not sure, but I'm thinking I am going to need some more variables in the mix.
The issue with taking in time played into account, is people can easily just sit at the title menu for as long as they want.
Right now the "pseudo" formula as it stands:
ScoreDivisor = 1000 (this value changes game to game)
Score = ScoreFromGame / ScoreDivisor
Max = Score * 2
Min = Score / 2
Gold = Random(Min, Max) (randomizes a number in between the min and max)
There's a bunch more for calculating the item rarity, and the item chance, but in this case, we are talking about gold. Maybe the time variable can fit itself somewhere in here?