13,413,365,441,180,119. I think I've at least taxed the maximum number of digits displayed. That was with about 1,010 bells and skipping some.
EDIT: Or... not? Lots of people have non-zero scores. Which makes no sense when it's just being added and multiplied. Whatever.
EDIT 2: I apparently beat my high score. But I haven't, because it limits the maximum number of digits at 17. So my actual high score of 1.3x10[sup]16[/sup] is probably quite a bit bigger. Seeing as my last highscore was about 4.3x10[sup]17[/sup] or 4.3x10[sup]18[/sup], the actual highscore could go as high as 1.3x10[sup]19[/sup] or 1.3x10[sup]20[/sup]. Unless there's a way to read the actual value of the highscore.
So yeah. Max score displayable: 9.9x10[sup]16[/sup] Max actual score: possibly bigger than the 64-bit.
And now I'm going to be late for my last lecture. Bloody game.
EDIT 3: Fail standard form is fail. Less likely to have broken the possible 64-but barrier, but the point stands.