Where a bit seems to be the lowest form of currency but how does the economy works I'm not too sure. I do find it necessary to point out that it is clear that Pinkie Pie was born the poorest of the mane 6 while Twilight was clearly born the richest, in fact I wonder if her family are nobles? Either way Pinkie is still the poorest by the looks of it yet she the one that point out Twilight royal authority when it seems that Twilight herself doesn't see it.