Many midrashim speaks on the greatness of the money spent by King achasverous in holding the 180 days party.
Is there any midrash that speaks on how much exactly did Achasverous spent on the party?
Not that I'm aware of, though the midrash does comment that in noting at the very end of the book of Esther that "the King levied a tax" is a polite way of saying that he had gone broke from all the partying. Similarly Rabbi Aharon Lichtenstein zt'l notes that the point of view here is just about those on the receiving end of such a lavish party, not all the work (likely including slave labor) that had to go into it; the Persian court didn't care about the "how" (contrast with something like the Mishkan). So we wouldn't expect to find that information!
In the same vein, Baal HaTurim observes that only twice in Tanakh is a king advised yafked pekidim -- "appoint officials." Joseph advises Pharaoh to plan during economic booms for busts, and in doing so makes Egypt a superpower; Ahasueros on the other hand is advised by his servant lads to put massive effort into skirt-chasing ... and his country is consequently in the red.