How much would a mnai during EB's time frame worth in equivilant to say...in US dollars? =/

And how much could 1 mnai get you?

Say, if i'm a reasonably well off (a nice estate, some slaves and workers tilling it for me, being able to provide myself gear for wars as a pezhetairoi...) citizen of Makedonia, and I'd like to buy some silk from Sinae, would that cost me an arm and a leg?