I have three reasonable book references on coins for this region and period, but they didn't come up with much this time. I have no doubt that some Serbian museum reference could give you more info. on this coin, but that won't give you a value.
For the benefit of the rest of us in the CCF, the best I could come up with is the Google reference 'The coins of Knez Lazar'.
My wild guess for a value of a slver Dinar of that illustrated in that condition would be in the region $40.